Light floats

Oldsailor, you guys must not have kept that boat ventilated, rode it hard and put it away wet. I've seen many ancient examples that are sound but were cared for properly.

 

I dont really see rotomolding as a valid approach for larger multihulls. The windrider used it with some success but even in that application it required an internal frame to carry loads and the boats were quite heavy for their length. I'm happy to be educated if there is some lightweight rotomolding technique I've not heard of though.

My old tortured ply 16' mosquito catamaran which was built in 3mm ply simply had taped seams relied on ply strength and was not painted or treated internally. It's true it did not sit in the water for any length of time but it did sit outside on its trailer in the weather with just the bungs out for ventilation. It was 20 plus years old with no signs of rot.

 

I was thinking a tube/cylinder down the length inside to stiffen it up. My Nicol is older than that with no rot but we are coating it as we go through the redo- its stripped and so on. This time of year we are shut down by the weather which is frustrating.

 

Information overload

But thanks
Sam, I am in complete agreement on the needed float size- big is best, however I build them.
These hulls, stretched, will have about 125' of surface area, (including decks) plus some internal bulkheads for the crossbeam attach points so the lighter I can keep the panels, the better. I also mess with sea kayaks, and I don't think roto-molded is possible at this hull size/volume, plus, this is a backyard/basement project- not production.
I live in the southern US, keep my boat in the water, and summer time temps are often in the F 90s-100, with 95% humidity, and then freezing temps in the winter. It is hardly possible to "properly" ventilate floats in these conditions, so any wood has to be extremely well protected. I really work at mine, and I still get rot every season starting on the underside of the decks and around the crossbeam saddles in stressed areas. Condensation happens! The main hull stays dry enough that I have not had many issues with it.
Since I can't change the weather, IMO, all small multi floats are better off built in foam/glass for lower up-keep. I am a part time cabinetmaker, and much prefer to work with wood, but for this use, I am very tempted to go with foam/glass. Labor and material costs look about the same, and I really detest the annual repairs on my floats. I am going to build some test parts out of both wood and glass, weigh them, and then decide.
I plan on using my old float set as a small power cat, stored on a trailer and covered. I even think the A-boards will still be useful in them- a power foiler B

 

You guys certainly seem to get more problems with condensation in the south. We get a few rain drops around the back hatch from certain angles but the only time more came in we noticed a kayaker visiting the boat! Sorry about the fracus you did say durability wasn't a issue....

 

I know of a few people who use those solar fan vents to force air through their boats in humid climates apparently it works well. If you want to make the ply more durable then do as oldsailor suggests and epoxy encapsulate the inside of the float you will pay a weight penalty but that could be worthwhile if it gives you the durability your seeking. Foam sandwich can be a problem if it uses very light laminate weights the core takes a pounding which will reduce the lifespan of the core material.

 

expendable materials

We do have humidity issues in the south- some thin all glass boats rain inside in certain weather. I use a solar vent on my main hull, and it works well enough to dry wet sails and line stored in the forepeak, but as my floats have watertight chambers, it would take six vents to do the job, and they would have to be removed and plugged each time I went sailing. I am much to cheap and lazy for that
I know that light construction of any type might not last, but if I can get five years or so with low upkeep out of them, I will be happy. I hope, in a couple of years, to get a boat something like Sam's new tri B

 

It was stored outside in the Canadian winter.

 

We bring wet sails and line inside to dry and always take time to ventilate because I'm too lazy to start from scratch every few years.....
Jeez Paddy, I know old fresh water boats that are still going up there after 2 or 3 decades!

 

OK, 20c worth this time,
I totally get the "why" as to foam sandwich given your climate.
I think your next stop should be a materials company willing to give you a laminate design. (via boat builder friend?)
I'd be looking at upping the core density from the usual 75/80 to 100/120 for the light skins.
Couple of advantages, compression strength obviously but also smaller cell size takes up less resin minimising the weight penalty of going denser.
Use Sglass on the external laminate.
Lay up on a formica table, outside skin and core. This will minimize finish work.
You could put in a rebate around the edge of the panels at this point to take the chine and hull deck/tape tapes.
Slice the core through to the outside skin if you need more bend.
Assemble and glass inside.
Foam bulkheads in 75/80 or lighter ? Wrap the laminate around bulkhead cutouts for a double layer inside the cutouts.
Peel ply everything !
That oughta do it !

Oh, paint it red !

 

You might want to contact Russell Brown

http://www.ptwatercraft.com/ptwatercraft/Trinado_molds.html

Personally I'd go for foam sandwich outriggers, 400g each side 8mm foam. I'd chose foam over ply because its easier to get a true round bilge hull which is best for inshore racing as you want to gain buoyancy as quickly as possible. A V'eed (even rounded V) hull has to heel more to get the necessary buoyancy, which adds to WSA, and reduces drive due to rig heel.

Richard Woods of Woods Designs

www.sailingcatamarans.com

 

Chainplates

I like the quality of the replies!
Any thoughts on chain plates? I have never attached anything substantial to construction this light. I am assuming glass or carbon fiber, but how do I carry the load to the float? Or another way to ask, how much of the inner and outer skins/core do I have to double up to take the stay loads.
I do build everything I can on formica with peel ply to keep parts light and easy to finish. These panels will stretch the size limits of my shop, but should be worth it.
RR, my boats name is "Pigs Fly", so it would have to be pink? B

 

If you are going to distribute the chainplate loads thru the skin by Glass or CF tape, you have to replace the core in that area with wood to carry the load equally to the inner and outer skin. If you don't do this you will be putting the foam core in shear----which is bad news.
We did this on the three B33s we built in foam sandwich and I know at least one of them is still sailing with no problems.

 

Make a bulkhead out of high density foam [Not wood] and attach the chainplate to that

 

I've never had carbon UD tows fail as chainplates on wood skins - in fact I'd suggest leaving all the liable-to-crush and delaminate foam out of the chainplate areas ... and put a few extra layers of box weave carbon over your glass base instead, before laying/fanning in your carbon tows. Loads on a B24 are not high anyway; light boat, (and your bis-version will be lighter again), quick to accelerate away from gusts and peaking high loads.