Lock Crowther 1962 Kraken 25 trimaran build and rebuild log

Epoxy keel/keelson was poured some time ago it's more of a deep fillet in this case. I'm very pleased with how strong it is bulkheads should go in next week and firm up the shape.

 

wait! think i knew that from your blog

its shaping up either way. is that 1"x1"(guessing) part of the jig you made for the top forming?


Barry

 

It's the same size as the gunwale strip 3/4" square but on reviewing the plans again I've realized that the crossbeam mounts are 1 1/4" square I'll probably just bulk up the Oregon a bit with some hardwood to that size to take the captive bolts that the beams are attached with. The bulkheads which are 3/16" ply had a sawn hardwood 3/4" nailed to the front face of the bulkhead in the original. That will be replaced with a structural fillet and some double bias glass.

 

My weekend boat work was put off due to an invite to go out sailing on a mates recently launched F82r "shockwave". Sadly the wind didn't cooperate for any racing but we had a pleasant afternoon rafted up on the water with some other club tri's on Westernport Bay.

 

A little more work on the tri this week. I marked a waterline on my main hull with the self leveling laser. A fantastic tool which makes the whole process so much easier. This is to help position the internal hardware with more precision.

I've cut and tabbed in the first bulkhead. This bulkhead is for the furler/genoa mounting and I've inclined it to be inline with the load. It's a double bulkhead with a 3/16" ply on both sides. I'll epoxy the inside of the cavity prior to closing it as It will be innacessible once the second part of the bulkhead is fitted. I'm going with the plan suggestion of a stainless strip bolted through the bulkhead for originality purposes. This bulkhead will have elongated lightening holes cut into it once glued in position.

To mark my bulkhead curves I use a handy Staedtler stationary tool. It allows you to bend it to shape and will hold in position for you to mark out on a sheet of cardboard.

 

looking good! Those tools are handy! I do curved stairs and steps all the time and use it quite a bit. If I have something real long I use bailing wire, cheap and disposable. Then if its something that has to be perfect I will staple tar paper flaps on the template and exact cut to shape with razor knife. Then just transfer it to part. Which is super handy trick if you have not only a funny shape to follow but have weird posts or beams in the way. Whats the plan for ventilation? through heads or top deck plugs?

Barry

 

I'm still debating the ventilation issue it's certainly important to have airflow through the hull. I'd rather not put a spin out cover on the bow for aesthetic reasons but will have one behind the roller furler base. The furler bulkhead will have cutouts so I'm hoping that will be adequate. I'm considering putting a limber hole under the bulkhead for easy drainage I've seen them done with a short section of PVC tube glassed in position to prevent any standing water remaining in the hull.

 

Ventilation

Gday Owen

I would urge you to consider having no access at all into the voids you make in the bow, stern and float areas. Well epoxied and with proper Gougeonesque attachments of fittings you need not have any access into voids at all. Epoxy coat them well and drop some Copper napthalate into the void as you seal it up.

Often adding the access creates the leak so I would use large wooden epoxied in place backing pads to tap into and composite chainplates as well to ensure the voids stay watertight. If you bolt you will need access and the leaks that will create.

cheers

Phil

 

I've been thinking rather than bolting the forestay fitting through I might follow the gougeon suggestion and just bed some machine type stainless screws in epoxy to hold the load. Most of the load will be in shear from the forestay my only real concern is the tow ring that will have to be attached in that area. I know they take a beating particularly when the boat is being pulled onto the trailer.

 

for those i still like a nice plate inside, changes load from pulling on hull skin, to pushing it from inside. And now while its open its easy to just take 2 plates and jam them in there, then weld them up. stainless of course. buddy recently did a nice job like that on older boat, with an extra mod, he did some plate outside as a scrub rail for hull.


Barry

 

Barry and I differ here. In the hinges I made for my little cats I had a similar problem. If you really want no water ingress then using dissimilar materials like steel and composite will eventually cause concern whereas uni glass will not.

You can reinforce the inside or underside of a laminate, hull or deck, with wood or glass, drill two holes through the skin and through the reinforcing and then stitch on a ring by tying chopper gun around the ring and through the backing plate. Keep on going till you have a nice composite chainplate to tie on anything you want - stays, jib leads, even my 38 footers hinging engine nacelle. I am sure it can handle the towing ring. Tie it on using four holes so it can handle both X and Y orientations and it will be tough as, cheap, look good and be watertight so you can block up the voids and have a leak free boat.

Most monos with the through bolted hull/deck flange eventually leak. Modern one offs dont because they don't bolt. Every bolt could become a leak so don't bolt unless you really can't avoid it.

cheers

Phil

 

actually you're right about the possibility of transfer down the actual bolts, Hadn't thought about that aspect. He epoxied them in but, im sure its only a matter of time. The adaptation came about from several incorporated fixes failed. The boat in question is a heavier motor sailer type, lots of gunkholing, ie yanking it up to shores took there toll on it. It wasn't just the trailer pulling but the see saw of pulling it in on a tree and such. Course in the end the biggest problem is production poly boat that epoxy will just never really stick to it.

Barry

 

Moving right along filleting more bulkheads and gussets in place at the beam landing areas. I'm thinking of reinforcing the tabbing with DB glass I will probably just put glass on the forestay and beam bulkheads as the deck support beams and gusset seem to be fine. The paulownia is reasonably strong but can tear out if enough load is applied over a small area.

 

Gday Owen

Are you not putting glass on the bulkheads? I would urge you to do so if not - even a very light 200 DB would be good.

When the Kraken was originally designed it was probably meant for cedar veneers or ply wood. The glues were nowhere near as good as epoxy. Even if you do not use any glass it should be much stronger than the previous build. BUT I would not be happy unless I taped the bulkheads in as well as gluing.

Have a quick test. Glue a piece of scrap onto a bench or scrap wood and cove it nicely. When cured tap it with a hammer. With a certain force the cove will crack and the join will totally fail. Epoxy - strong but woeful at impact resistance.

Then do the same with a light layer of glass over the cove and attached to the bulkhead proxy and scrap wood. You will need to pound away to get the thing to let go. The glass gives the joint huge impact strength.

As your hull is flat and will go fast I would be very willing to have some extra weight so that the bulkheads stay attached.

My 38 footer has 600gmDB tabs. I would want very light ones for your boat. You could try a technique Burt Rutan used on his planes - use sheathing cloth. He used to get some loose weave stuff and skew it with a friend but I just cut it at 45 degrees to the roll - cheap and light +- 45 cloth. It will weigh nothing but make the structure much stronger. (Watch out - it stretches like anything) Remember you won't have any water inside as the boat will have composite fittings so you can gain a kilo for strength.

cheers

Phil

 

Thanks Phil, I've more clarity in my mind in regards to the best approach now. I've decided to tab in with 400db over a fillet on the bulkheads. So you are suggesting it's a good idea to cover the flat face of the bulkhead as well with db glass? I've had some useful advice on composite mount on the bulkhead the general suggestion is to use glass uni's to spread the load over both the faces of the aligned bulkhead and then glass over with double bias which seems reasonable for the genoa mount. I was going to run with your suggestion on building the composite forestay mount and tow ring as it seems the best approach.

By the way I managed to weigh the hull properly the other day it's now 65kg which seems pretty good. Still a bit more structure to add around the daggerboard case etc but seem to be on track for a decent weight target at the moment.