Bayraider 17 bow shape.

[Anthony Huggett]

Can anyone offer advice on getting the bow panels down into the build cradle so they take the correct curve?

My current plan is to try screwing them into the mould (as in Andrew Denman's pictures on the Bayraider 17 - Basingstoke thread) and then epoxy fillet them to the cradle, so that the shape is retained and I can release the screws before glassing the inside. The problem being that the cradle is then glued to the boat and will take a lot of separating. I guess it is possible to unpick an epoxy fillet bond using a soldering iron. Does anyone have any better ideas?

[steve jones]

Hello  Anthony,

I made up a couple of pseudo bulkheads that mirrored the shape of the template, padded the side that fitted the lower panels and tapped them in place.

I could not get the exact profile but it was pretty close.


Steve Jones

[Anthony Huggett]

Steve,
     Thanks for that. Presumably you had to remove them again before glassing the inside?

Anthony

[Andrew Denman]

Hi Anthony,

Getting the bow shape is one of the more challenging parts of the build but not too difficult if you take your time.  I used a series of screws with ply straps and washers to pull the ply out towards the molds.  The ply straps spread the load - pics below.  I couldn't get right out to the molds ( about half an inch away in some spots)but fairly close.  Once there epoxy tag the outer hull to the molds and you're away.  One tip to help keep the bow area fair when doing this is to get a scrap strip of 6mm ply and use it to check for fairness of the shape you achieve in the bow.  Any "hard : spots will be revealed this way and save you plenty of fairing later on. - see pic below.

I would advise to sit the forward bulkhead in temporarily to pull the boat into the right beam before you epoxy up.



The epoxy tabs on the outer hull are very easy to remove later on with a heat gun and scraper.  If you don't have a heat gun I would strongly advise you to get one, preferably with variable temperature settings as it will be your most used tool in the build.  The epoxy softens with the application of heat and scrapes out easily so the heat gun is a great clean up tool but it is also fantastic for aiding cloth wet out when you sheathe the bottom and tape the seams.  

Epoxy is like honey - the colder it is the more viscous it is and if you have ever tried to wet out glass cloth with thick epoxy you will know it is a real pain to do.  By applying heat to the epoxy it will lower the resin viscosity and allow the resin to wet out the cloth more easily.  You will honestly halve your times doing this.  See attached picture - heat gun in one hand and squeegee in the other wetting out the hull bottom.

You can also use the heat gun to lower viscosity when clear coating.

Hope this helps

[Andrew Denman]

sorry the pictures dropped off the last post

[Michael Rogers]

Hi Andrew

Listening in, so to speak, on this thread, and with lots of epoxying of my own in prospect, could I raise two points from the helpful advice you have given?

1)  During the process of softening cured epoxy with a heat gun for cleaning up purposes, it is presumably not possible to confine the heating/softening process precisely and only to epoxy which is to be scraped off? Which means that some of the softened epoxy remaining in the joint or under the tape, or wherever, will harden up again when the heat is removed. Is epoxy which has cured, been softened by heating, and hardened again when cooled down, as strong and stable as epoxy which hasn't been treated in this way? Put another way, could structural strength and integrity be compromised at all?

2)  Using heat to reduce epoxy viscosity presumably also considerably shortens curing time? - which could be awkward, and obviously needs to be taken into account. Is this an indication to use slow hardener (I use West System) to offset this?

I have a heat gun, originally bought to burn off old paint (in a domestic context) but never actually used for that purpose. It's actually been quite handy for a number of diverse applications, but I haven't used it for epoxying - yet!

Thanks for sharing your expertise with us rookie builders - I'm sure much appreciated all round

SP Cadenza (and to-be-built TR12)

[Anthony Huggett]

I'd be a little worried about the effect of heat on the remaining epoxy as well. But looking at where Andrew has used the epoxy to tack to the mould, it is on the outside of the hull panels, not near the joints.
I wouldn't expect too much heat to get through the plywood to the inner sheathing, which will be in place before the tack is removed. The outer panel can always be sanded and recoated if necessary.

Regards,

Anthony

[Andrew Denman]

Hi Michael and Anthony,

The application of heat to soften epoxy is pretty common.  Gougeon Brothers, the manufacturer of WEST System had a great article on this exact topic a while back see http://www.westsystem.com/ss/if-you-can-t-take-the-heat/

The found that;

"Experience has also shown that while
heat tends to soften epoxy while it remains
warm, if WEST SYSTEM epoxy is not exposed
to damaging heat (exceeding 230°F/110 degrees C
for extended periods), it will return to
full strength when cooled to room
temperature."


If you use a variable temp heat gun you can control the amount of heat used quite easily.  Wood is a great insulator and if you heated the outer hull of the BR17 to remove some epoxy tags and it reached 100 degrees C on the outer surface, the inner surface would be nowhere near this hot.  Normally it only takes a few seconds of heat to soften the bog enough to scrape it off so it is really not an issue.

Another thing to think of is a dark hull.  I have measured the surface temp on dark hulls on a hot day and they are up around 80 -100 degrees C but the epoxy still retains it's strength with no issues at all.

WRT to the other query re using a heat gun to lower resin viscosity - it may slightly increase the rate at which the epoxy cures but as the epoxy is a very thin film it really does not appear to affect cure time much at all.  Try it - you will pleasantly surprised.

regards,

Andrew

[Anthony Huggett]

Andrew,
      Thanks for that. I had to break out the soldering iron last night after glueing the transom parts together. Very little heat seemed to be required to remove a couple of stuck-on washers.

Anthony