Need to make a female plug

I need to make a female plug of the front part of my catamaran, so that I can make a male plug which would be the replica of the hull for offsite build of the bulbous bows.

The female part must be done outside in 40-50 degree weather and must be done without harming the boat.

My basic sense says to use a gentle release tape over the hull and then I could use 3/4" wood and glue strips.

I have the first three stations, but not the zero or stem station, but I do have a plywood chain jig that could be attached to the first station. I also have the original canoe mould for the vee section forward, but that mould might be mishapen as was exposed to elements and it would not be super accurate as more glass was added after we flipped the hull, but it may be usable. I forgot how exactly the mould and frames intersected.

Also have hot glue.

Anyhow, any ideas are welcomed.

I'll probably dig the canoe mould out of the snow and see if I can make any sense of the fitment..

 

Here is a picture for posterity. All dev surfaces except perhaps some contours on bottom.

 

You could use plaster and cloth. I have used it to make repair panels by taking a mold off an intact hull.

 

Martin sent me a pro boat article featuring @Eric Sponberg .

I am wondering if perhaps the work must be done in situ.

It is possible the formers are supposed to tabbed to the hull...then the inside of the BB is laminated and tortured and then the final glass hand laminated in place.. This will be horribly weather dependent here. Then the inside of the bb can't be tabbed to the formers?

I suppose I ought to ask @Ad Hoc first...

This is me attempting to not be a pest and failing.

 

Do you need to make a plug?How about just taking a layup off the bows and using that as the basis for the job.It would help to mark a few reference points on the hull surface first so that they are imprinted in the gel.You will obviously make life a lot easier if the boat is levelled first and you can then attach a plywood spine and at least a pair of horizontal braces to the laminate you have created.The big question is which version of level you use and then determining the amount of additional buoyancy and it's distribution.The laminate and it's rudimentary framing can then be taken to a place where working on it is convenient and the normal process of plugmaking can carry on.

As an alternative,there may be a laser scanning service in your area that could scan the bow sections and present you with a CAD model of the surfaces.You could take these and amalgamate them with the shape of the bow extensions so that a business with a CNC router could directly machine the shape you require-in reverse.You then get to apply a finish and start making the parts,but you will obviously need to create an access hole to work through while laminating.It used to be the case that laser scanning was a rare and expensive business and it still can be if you require accuracy to microns.Last week I saw a youtube video showing the latest generation Iphone using it's built in LIDAR to scan things.A level of accuracy that is better than the thickness of a layer of bonding paste ought to be sufficient.

 

40-50°F is still in the epoxy curing window, so the simplest thing is to wax or tape the bow and laminate some cloth on it. Add a few foam battens with tape and it will keep its shape once demolded.

In order to work at such low temperatures you need to do it opposite as usual, use fast hardener, keep the mix in a tall pot, etc. Look at what your brand recommends, west for example goes as low as 41°F.

 

If you built a tub around the bow and made it go forward of the bow to the accommodate the volume of the bulb, say it is 4 feet forward of the leading edge of the bow. Then use spray foam to fill the tub you would create
a large rectangular foam block with the form of the bow in the back and enough foam in front of the bow to shape the bulb all in one piece.
I expect that you will hand shape this anyway?
The concave portion of the block of finished foam will of course be in close contact with the fiberglass hull which would not allow for any fiberglassing of the foam plug at this interface. If you need 1/4 inch of clearance
you might be able to tape the hull with 1/4 (3/16) inch thick tape, I am thinking the type that is sticky on one side and then a firm foam thickness. Similar to a firm weather stripping tape
Then you could glass the entire foam male plug?

Alternatively, to just create a male plug of the bow.
Just build the tub to carry to the bow, use the pour foam, remove the foam and tub from which creates the female profile, cap the back of the tub, use some type of release agent, and pour in another batch of expanding
foam..

 

My main goal was to recreate the hull upside down so I can build the BB in the shop in a controlled environment.

This foam idea is intriquing.

The hull is all epoxy and a combination of solid frp and foam core. The fairing is all epoxy and the primer is epoxy paint and the paint is either antifouling or two pak polyurethane.

The tub would be pretty simply to fabricate; somewhat onsite. I have 2# pour foam on the shelf. Since it is a catamaran, I could also check one vs the other just a bit for fitment with the plug removed.

The only, ahemm, sticky business, is release. I suppose I could wax it all four times and spray partall #10 on the boat, but not sure how wax will work with the antifouling. I am probably up for some repainting of antifoul. Just can't have it sticking and then later things must stick!

Then, I can take the tub to the shop and maybe paint the foam female plug with fairing compound a/o neat epoxy. Then make a male mould/jig call it what u like of the boat the same way. It sounds like a week of fiddling around to create a hull shape, but not too messy and all I need is a warmish day to pour. Maybe next week we might get a 60 degree day.

I'll see what the professional says about it all, but I like the idea. I have to see if I have enough pour foam for the first pour for sure and probably need to make the tub a bit odd shaped to reduce the foam needs for the first plug.

If he tells me I have to build the things in situ; that'll mean all of this was off, but the idea may help someone else someday.

Thank you to everyone for the contributions.

I have to trap the pour foam at the aft intersection. Maybe just some 1/2" or 3/4" weatherstripping foam would work...I also had some plasticine here, unless I pitched it in a shop cleanup day..

 

I probably need to mark the dwl on the plug or foam. It is 3" below the antifouling. So maybe I could do that with a couple layers of tape so a line transfers to the plug and then to the mould.

Then I can set it up level in the shop with a laser.

 

I also just realized I'll need to know how high above dwl to take off because the bb goes up above the waterline to shed water, so must be made higher for the finished product...

 

If they are symmetrical around the vertical that would work. Otherwise there will be a right hand and left hand side

Perhaps tape the hull with a tape that is smooth and easy to remove, (not Tyvek tape) and put the release agent on the tape. As above, if you are leaving the foam in, and are going to have a 3/16 inch composite build
up, you could tape the hull with a 3/16 inch tape.

If you are going to have the bulb foam filled, if you extend the foam tub forward, when you pull the tub off, you would then have the hull intersection formed as well as a connected chunk of foam to form
to the bulb.

The back of the tub would more than likely be ply so you could scribe the concave portion on to plywood. You can get this joint from ply to hull to be 1/8 inch with little work and less than 1/8th
with more effort. So even duck/duct tape would make up the joint.

 

My only goal is to get the hulls replicated in the shop. I'll wait to hear from the designer before doing so in case in situ makes more sense.

Both hulls are close to same, but one had a bit of a concavity in one spot that I faired out by hand, so perhaps minor delta.

I believe they are pretty close, but wondering if the tape idea makes some sense for a margin of error. 1/8" tape makes the female plug 1/8" oversized, then the male mould of the boat is 1/8" oversized and the final part is 1/8" too big all around, but would allow for bonding paste and small errors in fairing from one hull to the other. Bonding paste is higher, but touche'..