To balsa core or not to balsa core?

[DeepFrz]

The same care required to keep balsa from getting wet is also needed to keep foam from getting wet. Wet foam will degrade just as wet balsa will degrade. Not taking the utmost care in any cored hull to ensure that the core doesn't get wet is just asking for trouble. I'm sure that all good builders take great care to protect the core materials, no matter what they use, in their boats.

[DerekKelsall]

Hi Karl,

Not so.

PVC foam absorbs a v. small amount of moisture, (all materials take on some moisture) but does not degrade in water. We make no special precautions in using PVC, never have and the long term durability is indisputable.

My daughter has a garden chair - it was made as a first test of foam sandwich over the hull of Toria, with a bulkhead as the seat. All edges are cut, exposed and have been since 1965. The foam and fiberglass edges are abraded but no degrading of foam. The original outside paint, two pot PU is still good, though partly covered in green stuff. The bare fiberglass inside skin has a lot of the resin leached out in the sunlight.

In 1969, I made a concrete slipway in Sandwich in Kent. I used offcuts of PVC foam between runs of concrete. The foam still stands proud of the concrete having been washed by the tide for 40 years. I took a picture on my last visit to UK 5 years ago - the square cut edges are still there.

Best wishes,

Derek.

[DeepFrz]

So, you just drill holes through or screw into the cored deck to mount hardware?

[DerekKelsall]

Hi Karl,

No - again. Though it does depends on what the loading is on the fitting.

No light weight core will take the local compression involved when bolt fixing any fitting which is going to take a high load. A small hatch can be bolted through the two skins and the foam, providing the man doing the job knows to stop winding down the bolts when a snug fit is achieved. A winch or a cleat needs the foam replaced with a material which will take the compression load from the bolts. My rule - do not use plywood or any timber. A high density foam would be ideal but this is an expensive material and boat yards do not have it readily available. Build up a more solid pad replacing the core at each bolt or bring the skins together and add thickness in solid glass to achieve sufficient contact with the bolt. The solid pad can be cut from solid glass offcuts, with filler between or can be layers of glass (csm builds thickness effectively) built up in several stages.

We have developed means of fixing cleats and stanchions without using bolts to ensure no leaks. This includes cleats which are also lifting eyes for the crane to hook into for launching - avoid straps around the hulls. The crane drivers love them. Not yet found a way of fixing winches or tracks without bolts. Leaks can be avoided by bolting to a plate of solid glass and bonding that down to the deck - but adds weight.

Happy boating,

Derek.

[cat man do]

Originally Posted by DerekKelsall

We have developed means of fixing cleats and stanchions without using bolts to ensure no leaks. This includes cleats which are also lifting eyes for the crane to hook into for launching - avoid straps around the hulls. The crane drivers love them.
Derek.

Hi Derek, that is something I would love to have details on if at all possible to ad into my current build.

Thanks

Dave

[DeepFrz]

Those lifting cleats sound great. I take it that you use vacuum infusion, is that correct?

[mikereed100]

Hi Derek,

I'd like to second what Dave said. I have made fiberglass stanchion bases and will glass them to the deck so no leaks there, but I would love to see how you do your lifing eyes if possible.

Thanks,
Mike

[Blue Stocking]

Hi Derek,

In the 70's and 80's I was involved hands-on in building about 25 boats using Airex core with polyester skins. Am actually involved at this time doing up-grades on a 68ft double keeled glass bottom reef boat which we launched in 1975. The construction is as solid and dry today as when we put her in. Twin 4-71 power, all thru-hull locations had the foam cut away and the skins bonded and built up as you described, same for the decks. The boats ranged in size from 25 to 78ft.
For the sake of the non-believers FT is still sailing here in Bermuda as a dayboat in the tourist business

[cat man do]

Originally Posted by mikereed100

Hi Derek,

I'd like to second what Dave said. I have made fiberglass stanchion bases and will glass them to the deck so no leaks there, but I would love to see how you do your lifing eyes if possible.

Thanks,
Mike

Composite Chain plates which can be used as lifting eyes are easy enough but actual cleats? (I am assuming horn cleats)

Mike, the stanchion bases, do they protrude below deck at all or are they a route out core to innerskin and glass in tube?



Dave

[mikereed100]

Originally Posted by cat man do

Mike, the stanchion bases, do they protrude below deck at all or are they a route out core to innerskin and glass in tube?

Hi Dave,

I plan to glass them in using the second method that you describe. I figure they should be pretty bombproof once they are filleted and glassed in place. They are simple fiberglass tubes that I layed up using the stanchions as a mold.

Mike

[DerekKelsall]

Hi All,
Having started the balsa debate - on three forums - the forums are threatening to become a time consuming extra job!! - but good to see the responses.

To our friend in Bermuda - thanks for the info on the foam boats. 35 ft. FT was a bit of a compromise - to fit 28 WL class in OSTAR and under 35ft. in Round Britain. She went like a train for hours and then began to pitch and slowed right down. I can add that I believe the three near sister ships to Toria (1966) - Trifle, Leen Valley Venturer and Trumpeter were all still sailing on last reports from around the World. Names may have changed. Trifle was E coast US. Leen Valley venturer was in Venezuala. Trumpeter was on a Pacific Island.

Anyone here know the where abouts now of the above. Or of Sir Thomas Lipton - 58 mono, winner of 68 Solo Atlantic, which I have not heard of since the race. I am also trying to get an update on mono GB11 - 78 ft, first to finish in the first Whitbread around the World - and went on to race more times than any other and probably the most travelled yacht ever. - That was an interesting build in record time - by novice crew and as the largest composite sailing yacht at the time. - could only be done in foam!!

The lifting cleat is a horned cleat and the lifting straps pass between the legs. The stanchion fixing is just a length of solid uni glass rod, which can be made in several ways which is glassed in with a knee under and the regular stanchion fits over. We do not need to use resin infusion to make these parts.

I will come back with a location of where you can find pictures. Obviously, the cleat needs to be designed for the weight of the boat.

How much interest is there? - before I make any promises.

Derek.
Happy boating.

[cat man do]

Originally Posted by DerekKelsall

Hi All,

The lifting cleat is a horned cleat and the lifting straps pass between the legs.

I will come back with a location of where you can find pictures. Obviously, the cleat needs to be designed for the weight of the boat.

How much interest is there? - before I make any promises.

Derek.
Happy boating.

I for 1 am VERY interested Derek, my boat is my avatar, 50ftx24ft and should be around 8000-8500kg full load and 4700-5000kg dry

Thanks

Dave

[mikereed100]

As am I! My boat has a beam just under 8 meters which limits haulout facilities. Being able to haul with a crane would be very usefull.

Thanks,
Mike

[badlattitude]

Originally Posted by mikereed100

As am I! My boat has a beam just under 8 meters which limits haulout facilities. Being able to haul with a crane would be very usefull.

Thanks,
Mike

Is your boat a sailing catamaran or motor boat? If it's a sailboat couldn't you lift it by the chainplates?

[Cheechako]

It's a real dilemma. If you were builing your own boat you could core with 3-4" squares of balsa, which would avoid too much penetration when you (or someone) inevitably drills into the core to install something. Passport yachts used plywood core for decks for years. They used 3-4" squares of plywood and saturated/filled between t he squares. That way, when (not if) an intrusion occurs it's limited to that one square. On the other hand, the Celestial 50 was infamous for a badly saturated balsa cored hull.