The nice old gent who bequeath me that aluminium trimaran that looked more like a pirate ship also gave me a little aluminium sailing dingy.

I've found that my 5.8m winsurfing rig drops straight into the mast track so I'm going to clean the boat up and let my son learn to sail in it.

My question for the brains trust is about the suitability of using that expanding type foam found at Bunnings to refill the cavities under the seats. Is there a particular type that can be used to provide bouyancy?

Stripped and ready for refitting, so what do we reckon about using expanding foam from a can to fill the cavities?

The trouble with using expanding foam is that (1) it is probably not closed cell, which means it can absorb water (2) it will be difficult to remove it in the future (3) you lose storage space.
I suggest to turn some of the space into air proof and water proof storage compartments (in other words seal them and cut a water proof lid). For the rest fill the space with empty plastic containers that have lids and are waterproof. Then you have the best of all worlds.

That looks like fun, I'm sure he'll enjoy that! I don't have any experience with the expanding foams, but one major thing to look for in the specs is that it's closed cell, not open cell, for obvious reasons.

Looks great. Nothing to do with foam for flotation but would suggest the rig be supported by a suitable forestay and side shrouds. Realise its only a 5.8 sail but your windsurfer mast has the mast foot arrangement which is essentially a pinned joint allowing rotation about all 3 axes. Putting the mast into that mast tube with no other support could work in light winds but the inherent mast bending moment at the exit of the tube will be considerable and could cause the mast to fail in tension on the windward side or compression buckling on the leeward side. Obviously Laser etc masts are designed for this loading. Maybe a cheap old Laser rig is lying around............

Suggest securing the wishbone as high as it will go, with a suitable lashing system which won't slip down, and use suitable diameter dyneema to make a forestay and 2 sidestay shrouds located a suitable distance on the gunwale aft of the mast tube.

A neighbour had problems with the styrene foam that was in his quintrex tinnie and the dealer sold him some closed cell foam in sheets about 60 mm thick, which he cut and fitted to all the floatation spaces in the boat. Worked out rather well and easy to do.

Start collecting empty plastic coke bottles.
Pack them in and screw down the tops.
That is a real score. Great star in life for you and your son.

Nice looking dinghy. In addition to the other comments, I'd add that the most useful places for whatever type of buoyancy you choose are the stern and bow compartments. Water in those spaces will upset the trim more than in the other compartments. I'd suggest that whatever you do make sure the bow is sealed, or at least fill it with pieces closed cell foam big enough not to float out. Clark Rubber will have plenty to choose from. Also better for trim would be to use the middle compartments (under the thwarts) for heavy things like cargo, still dry but better in the middle in a capsize. Light ends make boats of all sizes handle waves better too. Put a towing ring on the bow too- good insurance and minimal cost.

As has been said, I would use closed cell sheet cut to fit, and 1st up I would try the air tight bow locker the stern and the two benches running across the ship and scuttle her and see how she floats if you need more buoyancy then do the side benches. I had a dingy that had its bouncy more aft and when it was flooded, it floated a stern up, a pain to get back on her feet and bail

Yes small dinghy bouyancy needs to be installed with thought - for this boat it obviously needs to be installed in the bow and stern volumes as above but as well judiciously elsewhere along the sides around midships out near the gunwales. Albeit too much bouyancy and wrongly distributed will mean that the boat will float too high when capsized and this will make an issue climbing onto the centreboard to right it and get back on board to bail it out............too little will mean a big bailing out problem if it is righted..........so both are potential safety issues depending on the conditions.............with a custom aluminium sailing boat like this suggest you sort out the bouyancy suitably. Are you going to fit self bailing venturis to it? So as to bail water as you go? see here

www.deckhardware.com.au/hardware/self-bailer/

Second the venturi suggestion. Either one, or one either side of the keel in the lowest points of the bilge. For bailing out, either a bucket or a juice bottle (2 L will do) with the bottom cut out. Or two, if two are sailing it. With a bottle you have both a handle (bail with one hand, steer with t'other), and something strong to tie it on and stop it floating away in a capsize. (Tongue in cheek- this is a former MJ sailor speaking) too much buoyancy can also spoil the learning experience. Making capsizes inconvenient makes a better sailor of you.

Yes good question. Would think a couple of knots speed would be needed.

There is an excellent article here; unfortunately it doesn't mention speeds. The article mentions that the Allen does not have a non-return flap.

www.ukmirrorsailing.com/index.php?option=com_content&view=article&id=1786&Itemid=1010

The Andersen bailer mentioned is here; it has the non-return flap which would presumably be an advantage as per the article.

www.arnoldsboatshop.com.au/bailer-super-max.html?source=googlebase&gclid=EAIaIQobChMIq5GQ0KLs6gIVE62WCh36rw8aEAQYAiABEgLzr_D_BwE

Note that for that aluminium dinghy all stainless fittings secured to it need to be isolated from the aluminium with duralac or Tef-Gel to avoid the aluminium corroding away due to galvanic corrosion.

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knot board said..

My question for the brains trust is about the suitability of using that expanding type foam found at Bunnings to refill the cavities under the seats. Is there a particular type that can be used to provide bouyancy?

You can use it if nothing else is available but every brand I tried in a can from Bunnings has shrunk with age.

Best to use a 2 pack polyurethane foam , something like trojanfibreglass.com.au/product/polyurethane-expanding-foam-liquid/
that won't shrink when cured and is flame retardant. You can work out the volume you need and mix only the required amount so no wastage and you don't have to cut off the skin which makes it even more waterproof. For large amounts you can pour it in layers and if you need to cut the skin off the top you can paint it with epoxy to give it maximum protection from moisture.

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garymalmgren said..
Start collecting empty plastic coke bottles.
Pack them in and screw down the tops.
That is a real score. Great star in life for you and your son.

+1. Great suggestion. If you get it wrong, or decide you want the storage back, its much easier to remove the bottles than trying to dig out foam.

As an alternative you could look at adding stability on the gunnels of the boat instead.

When you have a normal dingy from Walker Bay, when you add a sailkit you can also get an inflatable 'sock'that goes around the edge:
shop.inflatableboatparts.com/product/walker-bay-boat-rid-275-add-a-tube-kit-8-wb8-pvc-or-hypalon-pvc/

I dont know how windy it may be when your son goes out, your 5.8 m may not get the dingy heeling enough for the gunnels to go in the water, but it would add stability if it does.

Ive seen similar flotation collars made from pool noodles bundled together is a canvas sleeve, and lashed on.
Easily reversible, and not much outlay if you raid the local $2 shop of noodles.

Its a unique looking dingy, I'd be interested to see how stable it is, any idea of the weight?
Given the alu tri, do you think he made it himself?

its a fun project, and worth having a go.
Keep us posted.

Crusty that works, I made sponsons / fenders for a similar ding out of neolon epoxied it on been good for a few years now. Here she last time I hauled her out

Dumpster diving at the appliance centres yesterday

That foam would waterlog eventually. I would suggest converting the front compartment into a locker, plywood hatch with limber holes. Limber holes in the other compartments as well to drain the water. Use a plastic bucket for bailing, this will encourage the sailor to keep the boat upright. Make the seats into storage compartments with secure lids and fill all the compartments with plastic containers like 2L milk bottles etc.
When you get a chance post a photo of the welds. I suspect this old bloke may have welded this boat with a mig welder {splatter welding}.

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Ramona said..
When you get a chance post a photo of the welds. I suspect this old bloke may have welded this boat with a mig welder {splatter welding}.

Welding is fine.

Knot board, Ramona is right that sorta foam water logs eventually..... We used to wrap it in glad wrap, better still would be some of the cling wrap that's used in truck depots to secure pallets of bags etc, but it will still gets wet and falls apart after a while, the plaso bottles would last longer. But hey poke in it what you can get ya hands on, take it to the boat ramp or dam scuttle her an see where it floats or sinks, if you can bail from inboard when flooded or if you have to bail from overboard till the dagger board case is clear enough of the water line to allow the crew to clamber in ! Not a lot of people put much effort into the flotation bouncy of one off sorta dingys, it's a bit of fun and when it is canned in earnest you know what's gunna happen

then put the floaties on the side, or boat fenders, foam blocks, whatever, and see how stable it is if you sit on the sides and try to submerge it.
Depending on how heavy the young fella is, and if you plan to sail with him, your rig, combined weight and stability of the boat might end up suggesting you wont ever likely turtle it (with a bit of care).
(still good to know what would happen of course if you did).

Just on your rig, have a look at the landyacht forum. You will probably need to trim down the lowest section of your sail, to make it easier to duck under, especially if you have the centreboard partially up eg when coming back in to shallow water. The landyacht guys have good examples how to cut down the sail, depends how much you value the serverne.

I'd also consider putting 2 small U shackle through the front edge of the back seat or thereabouts, to bring your mainsheet bridle forward.
It will help you sheet in more directly, it was probably originally rigged up with a longer boom than your current windsurfer rig

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knot board said..

Ramona said..
When you get a chance post a photo of the welds. I suspect this old bloke may have welded this boat with a mig welder {splatter welding}.

Welding is fine.

Nothing wrong with mig welding aluminium. Once you try it after 5 minutes of training it's quick and fairly cheap. I reckon it would be easy to do a plate alloy dinghy these days.

You guys were right, polystyrene and expanding foam was a horrible idea. 2 minutes of fun followed by 2 hours of digging it all out again.
I can't find bottles that make an efficient use of the spaces so pool noodles it is.

My bold prediction is after word gets out Poodle Noodles will become the gold standard for underseat buoyancy in budget garage dingy industry. So easy to source and work with

By the way thanks for honouring me guys, I realise this is a forum for serious sailors but I'm having fun with this little project regardless

G'day Knotboard.
I recently lifted the starboard and rear floor panels in the rear cabins that are part of the foam filled chambers that is designed to keep you afloat if you end up with a big hole in your boat.
I was surprised to see it was all normal white closed cell foam similar in size to the pool noodles just squared not round. The whole underfloor had a bazillion of them, all carefully cut to fill out the shape of the void. It is so well done you can lie on it like a bed without any one piece distorting out of shape. There would have been 50 or 60 in that one are alone.
Talking to the yard they said they found this the best solution for providing buoyancy compared to other techniques they tried, the fact that it is a cheap solution and seemingly easy to work with just added to the appeal. So if your pool noodles end up deteriorating, that might be an option for you.
BTW, that's a cool tinny!
Cheers!
SB

ally rudder and tiller handle also?
jeysus

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crustysailor said..
ally rudder and tiller handle also?
jeysus

Yeah, the guy must have had shares in Camalco

I'm with shaggy it's a cool tinny, post us a pic when you flood it