Beam protection

[paul anderson]

Hi all

I removed the mast beam today, untying the lashings and noticed the top of the beams had been crushed slightly by the rope lashings. (rope indentations)

To avoid more wear and tear when afloat would it be a simple case of gluing some hardwood strips on top of the beams ?

Including those that are in the plans for the leading edge of the beams ?

Does anyone have a different solution ?

all the best

P.

[Omar M. Rashash]

How to explain?  Fiberglass/Epoxy composites are hard, but brittle.  If the glass composite is not thick enough to withstand the forces applied to it on its own, and the underlying material is softer, the composite will crack.  These cracks may not be visble to the eye and yet, be large enough to permit water intrusion and subsequent rot.  This is one of the reasons why, if you're going to apply epoxy filler under glass, you thicken with fibers or silica, not micro-bubbles. 

The idea of scarfing in hardwood has merit.  While high on the Janka Scale for hardness, Lignum Vitae (4500) would be both expensive and hard to epoxy.  In the western hemisphere, Ipe (3684) would be an excellent choice while Grey Ironbark (3664) would be a good choice in the Pacific.  I know the Ipe could be left unfinished and permitted to weather.  BTW, White Oak- Quercus alba (1360) should be avoided in composite construction because it is problematic to epoxy.

In traditional wooden boat construction, when boats had hulls that were saturated in water, the selection of timbers were based on their resistance to rot and their structural properties.  With the advent of Fiberglass/Epoxy composite construction, while structural properties are still important, rot resistance isn't.  If you're underlying wood structure gets wet now, you have bigger concerns than just rot.

[Jeremy Walker]

Paul: Fibre orientation on the bias (preferably double bias) and even long fibres wrapping completely round the beam would be best I think. Resin enough to saturate the fibres is all that is needed, but you could start the laminate on a bedding of epoxy/microfibre paste. This will take care of any voids, and could become a fillet to finish the edge of the fibre bandage.

Thickness?........easy enough to go overkill here and prevent any cracking. But with some engineering expetise it could be calculated.

My intuitive 'engineering' style tells me that a glass composite pad of equal thickness to a 3/8 or 1/2 inch hardwood pad, should be OK.......what do the engineers say?

[paul anderson]

All very interesting, I will make a test'' sandwich '' on Monday  and let you all know vs. hardwood.

cheers Paul.

[Patrick John McGrath]

IMHO , since the beam is softwood, all you have to do is round out the pressure point with a fine file or sandpaper so that the lashing distributes the pressure over a larger area. Then soak the wood of the beam with  a penetrating epoxy to bind up the wood fibres.

Three coats of any good boatbuilding epoxy will form a tough coating which will not crack, but should be protected from UV by two coats of urethane paint. The lashings themselves will show signs of wear before the wood under them. Just my 2c worth. :) 

[Galway Bay]

Paul, My original beams were softwood [fir ] and just painted. There was a silly amount of movement in the lashings so they were able to saw away to their hearts content for 10yrs. Once they had rounded off the corners to a radius say, similar to a teaspoon or such this stopped or became so slow as to not be noticed. Hard to describe exactly what radius but if you imagine the edge perfectly square , then rounded about the depth of the rope lashing that is it approx. The beams were replaced for other reasons entirely.

[paul anderson]

Well i have glued on some hard wood pads to the top of the beam and leading edge. Also the bottom rear facing part of the beam. basically just strips of hard wood that negate the chafing altogether from the beams themselves. i am happy with this solution and would recommend it to all new builders . The crushing that I had concerns about happened regardless of the fact that i had used heavy woven glass tape on the top of the beams when building them.

paul.

[Jeremy Walker]

This is the beaty of wood.......because of its relatively light weight (it floats) enough added meat or bulk allows for some of it to be sacrificial. Dense material like glass composite is often so thin that failure is inevitable. It really comes down to the thickness of the laminate.

[Jeremy Walker]

This is the beaty of wood.......because of its relatively light weight (it floats) enough added meat or bulk allows for some of it to be sacrificial. Dense material like glass composite is often so thin that failure is inevitable. It really comes down to the thickness of the laminate.

[laurent]

Why do there is hole Under and on the hiden side of the ply wood of tiki/pahi 26 main beams ? Is n't it a way for the water to go Inside the box ...

thanks

[paul anderson]

No idea mate,but i think it may help with the beam flexing?

[laurent]

ha ? ok , i was just about to close them .

So it is not because the seventies ? :

[paul anderson]

ha,ha.you also need to get to the dolphin striker bolts on the mast beam.The holes are good for smuggling also;-)