The waterline is
obvious at the transom...it's bottom, meeting with the hull, 257 mm.
above the base line; but at the bow it has to be deduced. In the 21' 9"
version of the slipper launch it is theoretically easy. It works out to
be 181 mm. below the chine at the stem. But because of the overlap
between top and bottom panels of the hull at the stem, and the
subsequent filling which was done to smooth it out, the chine can no
longer be seen. However, the water line is 680 mm. vertically below the
top of
the stem when the boat is in its floating position, ie. waterline
parallel to base line. So, as long as the upside down hull can be
arranged such that the bottom of its transom is 680 mm. higher than the
tip of the stem, and provided that the garage floor is level, it should
be possible to run a marker around the hull at transom bottom level and
reveal the true water line.
The first problem here is that the boat's bow is hanging out of the front of the garage by about 1.5 metres, and that the drive immediately slopes down from the garage floor. Therefore, the tip of the bow is at an unknown vertical level in relation to the garage floor.
To determine it, I lie the laser on the garage floor at the back, and shine it forwards to a line hanging from the bow. The spot on the line, which is 110 mm. above the drive in the bow's current position, is the height of the laser beam (20 mm.) above the garage floor. In other words the drive here is 90 mm. below the garage floor. The actual distance from bow tip to drive measures 860 mm., which means that the bow is currently 770 mm. above the garage.
The laser falls 110 mm. above the drive immediately below the tip of the bow, which means that this part
of the drive is 90 mm. below the level of the garage floor.
Provided the tip of the bow does not change its vertical level, the transom can now be raised so that its bottom is 1450 mm. (770 mm. + 680 mm.) above the floor and the boat should be in an upside down true horizontal position. The transom is currently 945 mm. above the floor, so it needs to be raised by 505 mm. Of course, since the boat is sitting on saw horses, the fulcrum for this rotation will not be right at the bow, so the bow level will drop a bit as the transom is raised, and the measurements will have to be repeated during the move.
Neither are garage floors ever level, so it helps to set up the laser on a truly flat platform, parallel to the ground. Its intersections with the hull can be marked to confirm the waterline's position. Raising the platform by a specified width and repeating the procedure will map out the area to be painted for the boot top. That can then be masked off with painters' tape and work can commence on painting the hull bottom.
Here is the boat with its undercoat on and the waterline being taped in.
In fact, the only reason the waterline needs to be marked at all at this stage is to protect the stem. The boat is about to be given its primer and undercoats. Beneath the waterline the paint will cover the stem, but above it the stem could remain bright, so the above waterline stem should not get any undercoat unless it is to be treated like Golden Glory's. Apart from that, the marking of the waterline could wait until the final coat of paint is being applied.
Two means of painting the stem
Top of Page
37. Painting
the BottomThe first problem here is that the boat's bow is hanging out of the front of the garage by about 1.5 metres, and that the drive immediately slopes down from the garage floor. Therefore, the tip of the bow is at an unknown vertical level in relation to the garage floor.
To determine it, I lie the laser on the garage floor at the back, and shine it forwards to a line hanging from the bow. The spot on the line, which is 110 mm. above the drive in the bow's current position, is the height of the laser beam (20 mm.) above the garage floor. In other words the drive here is 90 mm. below the garage floor. The actual distance from bow tip to drive measures 860 mm., which means that the bow is currently 770 mm. above the garage.
The laser falls 110 mm. above the drive immediately below the tip of the bow, which means that this part
of the drive is 90 mm. below the level of the garage floor.
Provided the tip of the bow does not change its vertical level, the transom can now be raised so that its bottom is 1450 mm. (770 mm. + 680 mm.) above the floor and the boat should be in an upside down true horizontal position. The transom is currently 945 mm. above the floor, so it needs to be raised by 505 mm. Of course, since the boat is sitting on saw horses, the fulcrum for this rotation will not be right at the bow, so the bow level will drop a bit as the transom is raised, and the measurements will have to be repeated during the move.
Neither are garage floors ever level, so it helps to set up the laser on a truly flat platform, parallel to the ground. Its intersections with the hull can be marked to confirm the waterline's position. Raising the platform by a specified width and repeating the procedure will map out the area to be painted for the boot top. That can then be masked off with painters' tape and work can commence on painting the hull bottom.
Here is the boat with its undercoat on and the waterline being taped in.
In fact, the only reason the waterline needs to be marked at all at this stage is to protect the stem. The boat is about to be given its primer and undercoats. Beneath the waterline the paint will cover the stem, but above it the stem could remain bright, so the above waterline stem should not get any undercoat unless it is to be treated like Golden Glory's. Apart from that, the marking of the waterline could wait until the final coat of paint is being applied.
Two means of painting the stem
Top of Page
The choice of bottom paint is wide open. Being a trailered boat, it does not really need to have an antifoul coating, unless there might be extended periods during which it is going to be floating, eg. on holidays. If an antifoul is chosen, it must be able to withstand being out of water for prolonged periods. Just such a product is International Paint's "Micron Extra". But at more than A$220 for the four litres necessary to coat the bottom, there is a lot to be said for leaving it on the shelf.
Topsides paint could be used under the waterline, provided it is tough enough to stand up to trailering, and it would not need to have a lot in the way of UV filters in it. Single pot polyurethane might be suitable, although Devlin's book is fairly disparaging about anything other than two pot systems, but then again, it is recommending antifoul bottom paint for anything bigger than the smallest skiff or dinghy. (Trailered boats are not specifically mentioned.) For maximum toughness (and maximum gloss and longevity) the two pot systems do seem better, but the choice will depend on the success of the preparation of the hull. The ultra-high gloss two pot paints will definitely show up the slightest surface flaws and you might as well save your money if you have a less than ideal hull.
In Ariadne's case I am happy with the sides of the hull, and reasonably satisfied with the bottom, but I see no point in using differing topside systems for above and below the waterline. It is either antifoul the bottom and topside the rest, or use the same topside paint throughout.
My final choice was between a two part polyurethane topside, with an antifoul bottom coat, (just in case of that holiday!), or a single part polyurethane throughout.
In the case of the former the paints to choose are International Paint's "Perfection" for the top, and "Micron Extra" for the bottom. In the latter it would be their "Brightside" all over.
The epoxy needs to be sanded with 240 grit paper to give a uniformly abraded surface, and then primed. "Primocon" is aluminium based grey primer, which acts as a binding layer between the epoxy and any antifoul. Only one coat of Primocon is needed on an epoxy coated boat. It is not suitable for sanding and should only be used below the waterline. It is followed by two to three coats of antifoul, in this case, "Micron Extra".
An alternative primer is "Yacht Primer", which can be used above and below the waterline under single pack systems. 3 to 4 coats might required under the undercoat, and it is sandable.
The drying and recoating times are dependent on ambient temperatures, and are spelled out on the packs.
My final choice was the Yacht Primer/Brightside combination, which means that the hull bottom and sides can be primed and undercoated at the same time, and to the same thickness. I will use a flattening agent in the bottom coats and paint the boot top over the place where topsides and bottom meet at the waterline.
So, the sequence on timber boats is as follows:
- Pre-primer
of 10-15% thinned Yacht Primer, 1 coat (if not already sealed). Not
necessary in Ariadne.
- Primer of
straight Yacht Primer, 3 to 4 coats (2 if epoxy sheathed already).
- Undercoat of Prekote, 1 to 2 coats.
- Mark the
waterline and boot top.
- Topcoat of Brightside, 2 to 3 coats.
But before any of that can happen, the freshly sanded hull has to be recoated with epoxy resin. I have decided that epoxy is a dog of a product to paint with on anything other than horizontal surfaces. No matter how much attention you pay to the drips and runs, they always reaccumulate. In an attempt to tip off the runs on the vertical side of the hull I have taken to making the last pass vertical too. Even that is no guarantee against horizontal waves forming, and if you are lucky enough not to have them you end up with vertical corrugations instead.
Vertical corrugations in the first epoxy coat.
I find that it makes
no difference whether you use a roller, brush or both. The first coat
of resin over a sanded surface has to be heavy to achieve a complete
coverage. It would be nice to be able to thin the first coat, but the
manufacturers warn against it. So the runs seem inevitable.As can be seen, the bottom of the hull is a lot smoother than the sides after just one coat of epoxy. There are a few dust specks showing through, but that is not a worry at this stage. It will be a different story with the top coat.
The runs from the first coat are even more pronounced the next day, but after the second coat is applied they tend to blend into the roller stipple anyway.
First
coat runs firstly shown up by sanding and then covered by roller
stipple.
On the subject of rollers, I was dubious about using cheap (presumably Chinese) disposable foam roller covers, thinking that they would disintegrate quickly, and need to be discarded more frequently. That would waste a lot of expensive epoxy. But I have found that they actually last longer than the ones I get from West for a fraction of the price, so I am sold.
Once the second coat is applied the whole hull and keel have to be re-sanded to accept the primer. Sanding freshly laid epoxy is a business in itself. It helps to wipe off the greasy bloom which forms on the surface, but even so the paper quickly clogs up with clotted resin. Aluminium oxide is a better choice than straight garnet paper, but still need frequent changing or cleaning.
Garnet paper (left) after only two passes, and aluminium oxide after 1 minute of sanding.
The hull bottom is
relatively straight
forward, as there are not many surface defects there, but on the side
the runs make it more difficult. I do the sides in two phases: the
first is to demonstrate where the corrugations are, and then the
second, with a new sanding disc, to rub them out. There is no point in
trying to make the corrugations disappear entirely. As long as they
lose their glossy surface they should be satisfactorily
abraded to
overcoat with the primer. After all, there are still at least six coats
of paint to go over the epoxy before the boat is complete, so the
miniscule depressions left after this degree of sanding should easily
be filled by subsequent coats.
The phases of sanding the sides: left,
unsanded, once sanded and twice sanded sections; middle, once sanded;
right, twice sanded.
When the chine is approached I abandon the power tool in favour of hand sanding, as it is easy to sand right through the finish and glass.
As sanding progresses up the hull bottom, a strip near the chine is left for hand finishing.
It is a cool and
gloomy Anzac day I was working on today, and by the
time I had finished half the hull, evening had fallen, and the light
was poor; so I left the rest for the next day. By the end of then I
hoped to
have the entire boat ready for the primer, and the first dramatic
change in its appearance since the epoxy first went on.
I won't be unhappy to see the last of those angry white eyes staring at me!
Now, the hull side bright strip had to be marked out and masked off so that it remained bright while the rest of the hull was painted. Incidentally, the matter of the bright strip, along with that of the boot top, is further alluded to in the Problems section, under the heading "Optical Illusion". I also taped off two strips on each side of the hull bottom, where the bilge runners will eventually go. I intend to glue and screw them into position, and I want to be gluing onto epoxy, not paint. But for ease of paint application with rollers, it is better to leave them off for the time being.
Masking for the bilge runners (left) and for the rubbing strake below the hull side bright strip (right).
The last job left
now was to sand the stem
and
keel. I finally decided that the stem will be painted up to the level
of the bright strip, not from any stylistic preference, but because the
opaque thickened epoxy I used to blend the hull side to the stem has
obscured some of it. To paint it wood coloured would be too artificial,
so I left the top 130 mm. bright and painted out the rest.
When the chine is approached I abandon the power tool in favour of hand sanding, as it is easy to sand right through the finish and glass.
As sanding progresses up the hull bottom, a strip near the chine is left for hand finishing.
In one or two
spots I have gone through to the glass, and these need patching with
epoxy so that the glass pattern does not telegraph throught the paint
finish.
I won't be unhappy to see the last of those angry white eyes staring at me!
Now, the hull side bright strip had to be marked out and masked off so that it remained bright while the rest of the hull was painted. Incidentally, the matter of the bright strip, along with that of the boot top, is further alluded to in the Problems section, under the heading "Optical Illusion". I also taped off two strips on each side of the hull bottom, where the bilge runners will eventually go. I intend to glue and screw them into position, and I want to be gluing onto epoxy, not paint. But for ease of paint application with rollers, it is better to leave them off for the time being.
Masking for the bilge runners (left) and for the rubbing strake below the hull side bright strip (right).
The last job left
now was to sand the stem
and
keel. I finally decided that the stem will be painted up to the level
of the bright strip, not from any stylistic preference, but because the
opaque thickened epoxy I used to blend the hull side to the stem has
obscured some of it. To paint it wood coloured would be too artificial,
so I left the top 130 mm. bright and painted out the rest.
A little bumpiness shows under the wet primer, but once dry the surface seems fairly good.
Because
there will be numerous coats of paint involved here, I am keen to avoid
getting a deep shelf between the painted hull and the masked off
portions. So I take the masking tape off after the paint becomes touch
dry. I will sand the edges lightly and reapply the tape before the next
coat, and so on until such time as the bilge runners are attached.
A word of advice
for
anyone contemplating using this paint: get a respirator. It is
extremely pungent and irritant to the airways. I hardly noticed it
while I was using the respirator, but when I took it off the fumes were
terrible. Apart from that the stuff is straight forward enough to
use. I continued with the disposable roller covers which I used with
the
epoxy, and they worked well. Brushing was easy too. Now, to get the
second coat on before two days have passed, otherwise I am in for
sanding the entire boat yet again.
After two coats of Yacht Primer had been applied, I changed to Prekote. The literature says that this undercoat should only be used above the waterline, but on the tin it only states that it should not be used in situations where permanent immersion is contemplated. I am advised that it is perfectly alright to use it under the waterline in trailered boats. The recommendation is that the second coat of Prekote should be mixed with a little of the final topside colour to make it easier to cover.
This is after the second coat of Yacht Primer, ready for Prekote.
Unfortunately, it does require that the primer be sanded before overcoating with Prekote, and that the Prekote itself should be sanded between applications. But these paints sand much more easily than epoxy does, and only a light scuff is needed with a relatively fine grit paper, 240 to 320 .
After removing the masking tape around the hull top side, I decided it was time to do some catching up with the epoxy, as the rest of the hull now had two coats of primer on it. The application of another coat of epoxy onto the bright strip revealed a problem with the previous coat, which had evidently picked up some sanding dust from the filling. Near all the scarf joints, where the fill had been used there was a milky discolouration. There is only one thing to do here: strip it back to the glass and start again. Hence the Prokote is left short of the bright strip. It would only be sanded away there.
Before and after epoxying the bright strip; it look alright from a distance...
...but close up it is a disaster.
After two coats of Yacht Primer had been applied, I changed to Prekote. The literature says that this undercoat should only be used above the waterline, but on the tin it only states that it should not be used in situations where permanent immersion is contemplated. I am advised that it is perfectly alright to use it under the waterline in trailered boats. The recommendation is that the second coat of Prekote should be mixed with a little of the final topside colour to make it easier to cover.
This is after the second coat of Yacht Primer, ready for Prekote.
Unfortunately, it does require that the primer be sanded before overcoating with Prekote, and that the Prekote itself should be sanded between applications. But these paints sand much more easily than epoxy does, and only a light scuff is needed with a relatively fine grit paper, 240 to 320 .
After removing the masking tape around the hull top side, I decided it was time to do some catching up with the epoxy, as the rest of the hull now had two coats of primer on it. The application of another coat of epoxy onto the bright strip revealed a problem with the previous coat, which had evidently picked up some sanding dust from the filling. Near all the scarf joints, where the fill had been used there was a milky discolouration. There is only one thing to do here: strip it back to the glass and start again. Hence the Prokote is left short of the bright strip. It would only be sanded away there.
Before and after epoxying the bright strip; it look alright from a distance...
...but close up it is a disaster.
The boot top on
traditional slipper launches is quite generous, taking up almost half
of the transom depth.
The boot top on Lisanne is not carried forward to the hull sides but on Lady of Iona it is.
If that line is carried forward onto the hull sides it gives the boats a somewhat overbuoyant look, almost like a hovercraft. A load in these boats tends to lower the stern more than the bow, so you get a rising hovercraft.
The boot top on Lisanne is not carried forward to the hull sides but on Lady of Iona it is.
If that line is carried forward onto the hull sides it gives the boats a somewhat overbuoyant look, almost like a hovercraft. A load in these boats tends to lower the stern more than the bow, so you get a rising hovercraft.
Admittedly it is unloaded, but Slipstream V seems to hover above the water...
...but loading Ayesha with passengers raises the bow out of the water.
Nevertheless,
that seems preferable to having no line at all, and there is something
appealing about the split transom in the water, so I propose to stick
with the convention and mark out my boot top the same way. That fits in
very well with my transom, which actually is split in its construction.
But
when its upper half is added later there is bound to be some sanding
and gluing which would be likely to damage any paint work on the lower
half; so for the time being I will leave the transom with no boot top.
The sides and bow can be painted in whenever it is convenient. As it is
topsides paint which is used, it could wait until the hull sides are
being painted, and I think that task is better tackled when the boat is
upright again, considering the bright strip and its separating rubbing
strake which have to be allowed for. So, right now, all that has to be
done with the boot top is to mark its position such that eventual
painters'
tape application will be easier. As it is likely to be some time before
the topside painting is done, any marking devices should be ones which
can be easily removed later. Ordinary masking tape is no good, because
its adhesion gets stronger with age.
39. Building
the New CradleThe final task
before
rolling the boat back upright is to build a new cradle to hold it in a
floating position, with its keel on. This can best be manufactured on
the upturned hull by selecting the stations under which you want the
supports to lie, building them with appropriate gaps to house the depth
of the keel at those points, and adding enough height to the stations
to make the boat lie horizontally when upright.
Two supports are enough. If you find the boat springing when you climb into it later, you can chock a wedge under the keel in the middle.
The supports should be high enough off the floor to allow the rudder, propeller and skeg to be put in later, or they should be put in at the time of rollover, with the stern of the boat being held high by the helpers. For later ease of access to the cockpit, the latter scheme is far preferable. But for the safety of the person putting them in, that job had better be completed before the celebratory drinks start!
Cradles, if there are to be only two of them, are usually positioned as near as they can be stations 2 and 8, assuming there are 10 stations in all. The Selway-Fisher plan does not use that form of station, because the hull panels had to be lofted on 305 mm. centres, and then bent to shape. However, an approximation of where stations 2 and 8 would lie if there were any is: between bulkheads A and B, and then between bulkheads E and F. Knowing the height of the bulkheads above the baseline helps in cradle construction, so I will place the supports directly under bulkheads B and E.
Bulkhead E is 95 mm. higher than bulkhead B, with reference to the base line, so I will make the supports with different sized height blocks added to them. The block for the rear one will be tall enough to accommodate the vertical height of the keel under bulkhead, E plus 95 mm. The block for the front one will be only the height of the keel under E, but with a slot deep enough to accommodate the depth of the keel under bulkhead B. That way, the boat will sit in its floating position, hovering above the garage floor, and with its keel clear underneath by the depth of the support cross strut.
The original lofting table which I used in January '06, now can be canibalised to makle the new cradle. The table aprons will make the cross struts, and the legs will become the vertical members. Keeping the structures low to the floor will assist in gaining access to the interior of the boat, which will be the centre of activity for the next few months.
The rear support is a little more complex than the forward, in that, unlike the hull under bulkhead B which is horizontal at the keel, the hull at bulkhead E is sloping backwards and upwards at 2.5°, as well as sideways and upwards at 2°. So the upright posts have to be cut on that compound angle. With the front support they only have to be cut to accommodate the V shape of the hull, at least the shorter posts do. The longer ones on the front support meet the hull at a different angle than the shorter ones, and I can see no way of working out what that is except by trial and error.
The short posts can be clamped together on either side of the keel, and the the long post/cross beam complex can be clamped to them. The amount of correction on the end of the long posts can then be estimated, and they can be trimmed to fit. Eventually a stable support will emerge, and as long as it holds the keel up at a level 95 mm. lower than the rear support holds its end up, all should be well on rollover day.
At the bow end the short uprights are measured for fit against the hull.
The short posts will not be attached to the stand until it is in position over the hull. That will allow
for any height discrepancy.
Front and rear supports in position on the hull.
Front and rear supports finished.
Two supports are enough. If you find the boat springing when you climb into it later, you can chock a wedge under the keel in the middle.
The supports should be high enough off the floor to allow the rudder, propeller and skeg to be put in later, or they should be put in at the time of rollover, with the stern of the boat being held high by the helpers. For later ease of access to the cockpit, the latter scheme is far preferable. But for the safety of the person putting them in, that job had better be completed before the celebratory drinks start!
Cradles, if there are to be only two of them, are usually positioned as near as they can be stations 2 and 8, assuming there are 10 stations in all. The Selway-Fisher plan does not use that form of station, because the hull panels had to be lofted on 305 mm. centres, and then bent to shape. However, an approximation of where stations 2 and 8 would lie if there were any is: between bulkheads A and B, and then between bulkheads E and F. Knowing the height of the bulkheads above the baseline helps in cradle construction, so I will place the supports directly under bulkheads B and E.
Bulkhead E is 95 mm. higher than bulkhead B, with reference to the base line, so I will make the supports with different sized height blocks added to them. The block for the rear one will be tall enough to accommodate the vertical height of the keel under bulkhead, E plus 95 mm. The block for the front one will be only the height of the keel under E, but with a slot deep enough to accommodate the depth of the keel under bulkhead B. That way, the boat will sit in its floating position, hovering above the garage floor, and with its keel clear underneath by the depth of the support cross strut.
The original lofting table which I used in January '06, now can be canibalised to makle the new cradle. The table aprons will make the cross struts, and the legs will become the vertical members. Keeping the structures low to the floor will assist in gaining access to the interior of the boat, which will be the centre of activity for the next few months.
The rear support is a little more complex than the forward, in that, unlike the hull under bulkhead B which is horizontal at the keel, the hull at bulkhead E is sloping backwards and upwards at 2.5°, as well as sideways and upwards at 2°. So the upright posts have to be cut on that compound angle. With the front support they only have to be cut to accommodate the V shape of the hull, at least the shorter posts do. The longer ones on the front support meet the hull at a different angle than the shorter ones, and I can see no way of working out what that is except by trial and error.
The short posts can be clamped together on either side of the keel, and the the long post/cross beam complex can be clamped to them. The amount of correction on the end of the long posts can then be estimated, and they can be trimmed to fit. Eventually a stable support will emerge, and as long as it holds the keel up at a level 95 mm. lower than the rear support holds its end up, all should be well on rollover day.
At the bow end the short uprights are measured for fit against the hull.
The short posts will not be attached to the stand until it is in position over the hull. That will allow
for any height discrepancy.
Front and rear supports in position on the hull.
Front and rear supports finished.
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Problems
shows higher
resolution shots as well.