7m tri beams

[CTMD]

Rather than fully machined moulds get soemone to cut out 2d templates which can be formed into a jig. Much cheaper.

[bushsailor]

Originally Posted by bruceb

Yes, any details/pictures of your attaching points on both the inner and outer hulls. I keep worrying about the loads on the forward crossbeam particularly. Fore and aft as well as vertical loading; falling off a wave sideways at 15+ knots has to impose a shock load several times the weight of the boat. I have broken the forward pylons out of Hobie hulls several times. Many failures on offshore tris seem to be around the forward outer beam/float area. I don't want to add to the statistics Are you planing for boards or rudders on your floats? Bruce

I am slowly doing some proper drawings of the boat but none are complete. They are all done by hand at present.
Fore and aft bracing is done by vectran bracing diagonally under the nets.
Beam float mount is by going through the float deck onto the side of the bulkhead underneath (in the hull). That way there are 2 stress points instead of one. (bulkhead and deck).
Board is in centre hull. Rudders are in floats. We discovered that rudder in main hull lets go over about 18knots.
Thanks for the advice Chris, it all helps.

[bruceb]

Does anyone know the layup of 24' Grainger or Corsair beams? I have also wondered how much tension (if any) to pull the uni fiber layers while they are curing. I am used to working with glass and wood, but I am a novice at loaded beam construction. Thanks for any help, Bruce

[idkfa]

What type of joint at the amas are you considering? Are you using bolts through the deck or some sort of interferance joint, where the crossbeam and ams plug into each other and the loads are passed through the material in contact and not the fasteners.

Bit harder to fashion but may be worth it? If the crossbeams extend immovably out from the amas, they may handle the fore aft loads making your diagonal stays just added insurance.

[bushsailor]

Originally Posted by idkfa

What type of joint at the amas are you considering? Are you using bolts through the deck or some sort of interferance joint, where the crossbeam and ams plug into each other and the loads are passed through the material in contact and not the fasteners.

Bit harder to fashion but may be worth it? If the crossbeams extend immovably out from the amas, they may handle the fore aft loads making your diagonal stays just added insurance.

I agree, below is part of another post.
Beam float mount is by going through the float deck onto the side of the bulkhead underneath (in the hull). That way there are 2 stress points instead of one. (bulkhead and deck).
As per previous post why is the centreboard so far forward on many tri designs? Someone must have some ideas

[ThomD]

Board position:

I think there are two reasons, one is better upwind performance which is traditionally a Bugaboo with tris, even if well laid to rest. The other reason is the ama digs a hole as the wind blows, which counters weather helm, but possibly makes a forward position for the board better.

On beams just plain beams without folding capacity, 4" Al with 1/8" and wires; 6" with 3/16" walls no wires, 6" square wood with 1" walls, no wires. With the wood you can fritz around with the wall thickenesses, and proportions of the tube to be a lot more efficient.

[bruceb]

I have a Buc 24 that I experimented some with board position last season. The top of the board is mostly cut away so it can "swing" fore and aft in the trunk. Center of area can be moved forward about 0.4 m from stock. My boat has a tall rig and shorter boom, so my sail center is slightly forward of stock, but the boat really liked the board in the forward position. Pointing improved by 1-2 degrees made good and the balance was better also. It does load the rudder more, but the control is better. (I have built a much longer rudder for this season) Both foils are lifting surfaces, it just forces the rudder to be a little larger and carry more of the load, which seems to help control on all points of sail. Most small tris and sport boats are carrying a lot of aft rake on their rig which seems to indicate that their boards are too far aft . I might even try moving my mast back about 0.1-0.2m, I know at least one other modified buc 24 has tried it. Of course this is an old design, but the results probably are relevant for most tris. I am still following the beam design/construction thread- I hope some more experienced people post Bruce