Q: Making mini-deck for mast partner in thin fiberglass hull

[almot09]

Long-ish post, please see the photo with mock-up below.

The problem: narrow sea kayak, has a thwart with floats (aka and amas). Aka has a mast partner - black collar, but the struts holding aka to the hull allow some play, mast is leaning to the lee. Need a board with a hole for mast.

The plan:
Red fiberglass angles will be attached to the coaming with #8 machine screw studs for sprayskirt fasteners (original short studs are removed). Onto red angles the wooden deck will go (ignore wooden blocks, this is where the deck will be). I'm thinking 3/4" plywood or 1" board, same thickness. Deck will be less than 10" wide at the widest, 32 sq ft sail.
Q 1: At this small deck and sail does it even matter, ply or wood?

Will pour some G-Flex in curvy gaps ~ 1/8" between the coaming and red angles, as angles don't conform well. Maybe will add one #10 screw between the two #8 studs (studs are 7" apart), couldn't find stainless #10 machine screw studs 5/8" long.
Q 2: Overthinking with added #10 screw? There is no vertical load, #8 screws are only to prevent the deck from falling out. Hate drilling holes in the boat .

Can put the board on top of the coaming, scribe underneath and file until it fits. Or a carpenter compass? The coaming slopes here, walls are not vertical at the fore end, not experienced with compass but this slope sounds like a file work.

Q 3: Should I bother extending the deck fore, beyond the angles, all the way to the fore end, to make those 1/8" coaming walls stiffer/stronger?

The biggest Q: how do I center the hole to make the mast go from the thwart collar to hull cup? Hull cup and collar on the thwart are already there, mast rack is set. Cut an oversized deck, cut the mast hole, put it on the gunwales, put the mast through, scribe and cut the deck to make it fit?

A thought. Sailmaker has a nice plastic (Delrin?) mast partner to put on thin fiberglass deck of a kayak, a short tube with flange, exact diameter for the mast, with another flange underneath, to sandwich the deck in between. I'm making a deck, might get this part as well?

Please don't laugh if I missed anything IMG_20230104_151729.jpg

[Toxophilite]

I'm not going to laugh, but this really seems like a non wooden boat question. Am I right? Is this a fibreglass kayak you're rigging up?
If so you might be in the wrong place, likely there's a kayaking forum that would have way better specialized information.

Also I have to ask, what is an aka and an amas? Are these kayakian terms?

[robm]

He is asking here because wooden boat people actually build, modify and maintain their boats, and probably have a better idea how to do what he wants to do. I am not really getting what you want to do, so I hesitate to respond.

[Todd Bradshaw]

Perhaps a wider-angle photo would help us figure out what exactly you are planning. Tox, amas are the floats and akas are the crossbeams for a trimaran.

Red flags so far: Drilling holes in a cockpit combing of a fiberglass kayak seems like a pretty structurally dangerous operation. Also, an awful lot of the jobs that seem to get assigned to G-Flex are not the uses that G-Flex is designed for or is very good at. I'm not sure exactly what the function of it would be here, but I really doubt that it would be the best epoxy product to use.

[P.I. Stazzer-Newt]

So many questions..

Is this a mast partner or a mast foot?

Stayed or freestanding?

A bolt on spraydeck..... WTF.


Todd's call for wide angle pictures to show what the whole project looks like makes sense, I'd like to see a written description of sailing conditions you hope to meet.

[johngsandusky]

I've sailed a couple of canoes and kayaks that were not originally designed or built to sail. My method has been to attach a mast step to the hull and clamp or strap the thwart to the gunwales or coaming. A board crosswise under your deck can be lashed to the thwart and grip in place. I have not used any outriggers, amas, akas or floats, which means a smaller sail. With a little ballast and luffing when necessary I keep her upright. My style of rig is lower stress and probably lower performance. I've used rigs from 25 to 55 sq ft on boats from 15'x28" to 17'x39", most often a 36 sq ft BSD Classic Canoe Sail.
Keep thinking and studying, you'll find a solution. Keep us posted.

[almot09]

Todd, G-flex will only fill narrow gaps ~1/8' between fiberglass coaming and red fiberglass angles. The angles will be held to the coaming with snap fastener machine screw studs https://www.sailrite.com/Snap-Fasten...l-Plated-Key-I (see black screw head on the starboard coaming, this is where one of the studs will go). There were studs here before, I'm replacing them with longer ones to hold the red angles as well as serve as snap fasteners, using same #8 holes that were here before. No new holes in coaming, alright. Angles are straight, coaming is curved here, close to the bow, ends of the angles (where bolts/studs go through) are flat on the coaming, but middle of the angle has a gap from the coaming, this gap I'd like to fill. Not much load-bearing on G-flex, some compression load from this my plywood mini-deck (if I make it fit snag), not much of a gap. I have G-flex, could use it - you think I should fill this with something else?

Johnsandusky - yes, this is a BSD rig.

P.I. Stazzer-Newt: There is a mast step at the bottom, see the photo below. There is a mast partner - sort of - on the thwart, but it's leaning to the lee together with the thwart because of how the thwart is attached to the deck-hull seam. I'm trying to make a more rigid mast partner by placing a plywood on the 8" long 1/8" red fiberglass angles that are attached to the coaming with long snap fastener studs (yes, bolt-on studs, see the link above). Ignore wooden blocks on the photo, they are just holding red angles for now.

As the mast partner on the thwart and mast step at the bottom are already there, the new partner/hole (on the ply on the red angles) needs to be exactly aligned between bottom mast step and thwart mast partner - this is what complicates the job - and my narrative .

IMG_20230104_151848.jpg

[johngsandusky]

I can see from this picture what you mean. It makes sense to me, especially considering how narrow the coaming is at the thwart.
The first canoe that I sailed is a Tom Hill glued lapstrake. Light weight and without frames, I split one of the laps sailing in too much breeze. That taught me to luff the sail slightly in gusts.

[JimConlin]

Back up twenty feet and think about the forces involved here. How are they transferred to the rest of the boat?
Wind pushes the sail which pulls the mast, which tries to tip the boat over. Where can the force of the mast (Designers might use the word ‘heeling moment’ or ‘torque’.) be transferred to the rest of the boat? If this were applied to the coaming, it might be a force of over 1,000 lbs. This would tear the thin fiberglass deck apart in short order. The other places where such a torque might be applied are by stays from the mast to the ends of the akas or to the side of the hull near the mast. THe first is easier to implement
You need to consider the fore & aft dimension, too. Stays to the bow and maybe the stern.

You might also consider another approach.


Take a golf umbrella.

[almot09]

Jim, the deck will be 3/4" wood wedged between starboard and port coaming, close to where coaming becomes a kayak deck. 1/8 fiberglass angles - red pieces on the photo - are to keep 3/4" wood from falling to the bottom. People here will correct me if I'm wrong but the heeling moment is mostly lateral, not vertical.

In a decked kayak this king of rig with sail up to 36 sq ft is installed through the OEM fiberglass deck that is 1/8" thick, with a mast partner - a piece of Delrin tube with flanges below and above the deck, so the deck is sandwiched between the flanges, with 3 machine screws through the flanges. I'm merely building up the missing deck. But - point taken, I might glass 3/4" wooden deck permanently to the supporting angles and to the coaming.

[johngsandusky]

My BSD Classic 36 rig works well in a Tom Hill Ultralight 15' and Folbot Yukon 13', both around 40#. Sitting on the gunwale in the Hill canoe with no frames was too much and split a lap. I think your kayak would twist before breaking. My former Folbot Super used a 55sqft lateen with shrouds to the ends of the mast thwart. Part of the reason I use webbing to attach the thwart to the gunwales is that they have some give. Keeping in mind that these boats were not designed or built to sail, I use caution in how much wind I sail in, and I luff in puffs.

[almot09]

I think your kayak would twist before breaking. My former Folbot Super used a 55sqft lateen with shrouds to the ends of the mast thwart. Part of the reason I use webbing to attach the thwart to the gunwales is that they have some give. Keeping in mind that these boats were not designed or built to sail, I use caution in how much wind I sail in, and I luff in puffs.

Ah yes, that thwart with mast collar/partner. 55 sq ft is huge, on this kind of boat. Still, I felt safer - in terms of breaking the boat when sailing - in a flexible folding Feathercraft than in this kevlar open-deck kayak. BSD design blocks fore-aft movement of the mast, struts attached to hull-deck seam take care of that. (Soon to be) added mast partner in this mini-deck will block heeling moment and transfer it to the coaming, distributing the load over 7" length of coaming.

As I mentioned, coaming is curvy and the red angles supporting the future deck are straight, creating a narrow gap few inches long. I'm thinking to fill the gap with either G-Flex epoxy or regular epoxy with filler.

Q: Since Todd disapproved G-Flex for this application, I'm scratching my head what to fill the gap with. Is G-Flex too flexible to transfer the load onto (also flexible) 1/8" FG angles and 1/8" thick coaming? Marine epoxy with polyester filler? I hate buying a quart of expensive product for filling a fraction of cubic inch of space.

[Breakaway]

A

lso I have to ask, what is an aka and an amas? Are these kayakian terms?

Common terms in describing multihull boats.

Kevin

[JimConlin]

They are trimaran terms. Polynesian, I think.
Floats are amas.
Cross beams are akas.
Main hull is vaka.

[johngsandusky]

Are you bolting the angles to the coaming? Perhaps wedges glued between.

[almot09]

Are you bolting the angles to the coaming? Perhaps wedges glued between.

Yes, angles bolted to the coaming with 8-32 fastener studs, so that I could still use the skirt. There was a skirt there before, only thuds were sort of riveted to the hull, not bolted. Would prefer #10 screws but 5/8" studs don't come in #10. Filling the gap with epoxy (plus filler?) would make a perfectly fitting wedge, no? Maybe will ask about wedge/filler in a separate thread, I feel that local community has lost interest in this thread

[johngsandusky]

I think the bolts will hold it well if they go through enough glass, or with sufficient backing. Epoxy would be icing on the cake.

[adamarthurryan]

Would prefer #10 screws but 5/8" studs don't come in #10.

Easy to cut down longer studs or threaded rod with a hacksaw.

[adamarthurryan]

Taking a crack at your q's in the OP.

Q 1: At this small deck and sail does it even matter, ply or wood?

Ply makes sense to me because of it's more or less equal resistance to splitting on both axes. Vs. wood which is weaker perpendicular to the grain.

Will pour some G-Flex in curvy gaps ~ 1/8" between the coaming and red angles, as angles don't conform well. Maybe will add one #10 screw between the two #8 studs (studs are 7" apart), couldn't find stainless #10 machine screw studs 5/8" long.

Q 2: Overthinking with added #10 screw? There is no vertical load, #8 screws are only to prevent the deck from falling out. Hate drilling holes in the boat .

If you're feeling #10 is better, just get some long ones and modify with a hacksaw. Or use threaded rod, etc. Re. vertical load, idk, there is probably going to be all sorts of twisting force - easy to imagine the partner getting popped out. Also, I imagine as the mast top is pushed to leeward one side of the deck will tend to be lifted up from the coming and one side will be pushed down.

Can put the board on top of the coaming, scribe underneath and file until it fits. Or a carpenter compass? The coaming slopes here, walls are not vertical at the fore end, not experienced with compass but this slope sounds like a file work.

Yeah, lots of techniques for fitting. I'd make a template in 1/8 doorskin probably. Fit it just right on those red angles and trace it to the stock. Then take off bevel angle with a small bevel - a couple hacksaw blades riveted together with a nail works for this. Filing makes sense for final fitting. Or a block plane.

Q 3: Should I bother extending the deck fore, beyond the angles, all the way to the fore end, to make those 1/8" coaming walls stiffer/stronger?

I think yes for sure.

The biggest Q: how do I center the hole to make the mast go from the thwart collar to hull cup? Hull cup and collar on the thwart are already there, mast rack is set. Cut an oversized deck, cut the mast hole, put it on the gunwales, put the mast through, scribe and cut the deck to make it fit?

That was my first thought. If you make a pattern you could do this with the pattern. Also, possibly the hole will not be perpendicular to the deck. Depends on the geometry of everything.

I guess an obvious question I have though is why not just shore up the existing system to make it more rigid?

[Thad Van Gilder]

I'm not going to laugh, but this really seems like a non wooden boat question. Am I right? Is this a fibreglass kayak you're rigging up?
If so you might be in the wrong place, likely there's a kayaking forum that would have way better specialized information.

Also I have to ask, what is an aka and an amas? Are these kayakian terms?

On a trimaran, a aka or vaka is the center hull. The Amas are the side (smaller) hulls.