Small Day Boat Refurb Discussion Topic - Buoyancy

[oldbilbo]

Reading Lakey's OP and subsequent comments again, I'm wondering if there isn't benefit to be had by use of a couple of those Italian inflatable boat rollers. One of these strapped under each side bench should provide enough extra buoyancy, in the right place, and they're both cheap and robust enough.

They'll also do 'double duty' should you need to haul the boat ashore somewhere, or lie alongside a pontoon/quay/jetty. And they can be deflated, taken home, and sold on here if you decide they're not traditional enuff.....

 

[dancrane]

Nice thinking Bilbo; I bought one a few months ago to help cope when landing the boat singlehanded, without leaving her bashing the beach in the breakers...

...I bought the 400kg-rated Plastimo. It's a nice idea - but it looks and feels like a pool toy. I can't imagine any beach where I'd want to trust the Osprey's weight on it - in fact I plan to reinforce it with some of that swimming-pool cover material, like heavy-duty bubble wrap, before trying it out. The fabric just doesn't look tough enough as it is.

As a buoyancy bag I'm sure it'd help - although despite its considerable size, it must represent less than 750 Newtons.

 

[Avocet]

Just to ad my 2p worth:

1. I WOULD glass the bearers in - with quite a lot of glass. If water gets in and they DO eventually rot, you'll at least have some (in effect) nice hollow top hat stiffeners for your hull.

2. No real opinion about buoyancy, but intuitively, as it's so easy to reclaim the "dead" space over the bow locker, it would seem sensible to do it (and the transom so it stands half a chance of floating level if the worst happened.

3. I was surprised, in the drawing in the OP, to see how high the internal floor was. I'm wondering if it provided useful lateral support for the centreboard casing? Without a floor to brace it sideways, won't it try to bend itself out of the bottom of the boat? At the very least, I'd be worried about stress cracks forming around the root of it.

 

[Lakesailor]

Just to ad my 2p worth:

1. I WOULD glass the bearers in - with quite a lot of glass. If water gets in and they DO eventually rot, you'll at least have some (in effect) nice hollow top hat stiffeners for your hull.

2. No real opinion about buoyancy, but intuitively, as it's so easy to reclaim the "dead" space over the bow locker, it would seem sensible to do it (and the transom so it stands half a chance of floating level if the worst happened.

3. I was surprised, in the drawing in the OP, to see how high the internal floor was. I'm wondering if it provided useful lateral support for the centreboard casing? Without a floor to brace it sideways, won't it try to bend itself out of the bottom of the boat? At the very least, I'd be worried about stress cracks forming around the root of it.

All good points.
1) : I intend to use a a fair bit of glass. I originally thought about hardwood bearers, However hardwoods are tricky to bond to in some cases (being oily wood) so I will probably use ply.

2) : Yep that's about where I stand at the moment.

3) : Yes. The centre board is pivoted very close to the hull bottom so may not have much leverage, however the mast tabernacle is mounted on top of the case.
I am going to glass in some triangular knees between the hull and the centreboard case. I'll cut a radius in the bottom corners of the knees to allow bilge water to flow forward to the bilge pump pick-up.

 

[srp]

I wouldn't use wood for the bearers. I have seen a glassed in bearer split the grp all the way along its length when the wood expanded. I've also replaced bearers that have completely rotted and caused osmosis inside the hull as they have been wet for years. Use closed cell foam as a core or former, bonded in with dabs of p38 just to hold it in place, then several layers of glass and epoxy, maybe aiming for a finished thickness of around 8mm. Just like any beam, the difference in strength between hollow and solid is not worth the extra weight, and certainly not the chance of it splitting open.
Of course, if you're dealing with a bit of an old wreck that you just want a couple of years of fun from, then you don't need to be as fussy, but for a proper job thats how I'd do it.
Oily woods are a bit of a myth in my view - I've made loads of epoxy bonded laminated tillers with teak and iroko and never had any problems. Sometimes they get a quick wipe with acetone but mostly not.

 

[Lakesailor]

I'll look at closed foam. It seems a bit more expensive than I was planning on. A 2" thick sheet big enough to cut what I plan would be over £50. Plus I would probably use more mat and resin which would be a further cost. The boat is nearly 25 years old so I am not expecting any mods to outlast it.

 

[fisherman]

Foam from my local GRP supply is expensive, he suggested using celotex, which I do anyway. My top hat structural frames in my FV are foam, as are the engine beds, 38 years on perfectly good.

 

[Searush]

I'll look at closed foam. It seems a bit more expensive than I was planning on. A 2" thick sheet big enough to cut what I plan would be over £50. Plus I would probably use more mat and resin which would be a further cost. The boat is nearly 25 years old so I am not expecting any mods to outlast it.

Given that it may not have been in the water very much in that time it may well last another 50-70 years of abuse. So it will probably out live you by a few decades - anyway, you'll be selling it again in 18 months given your current track record so far.

PM me when you do decide to sell it, I may be ready for a day boat myself by then.

Oh & why not a central thwart to support the centre board, should be a good rowing position at a guess?

 

[Lakesailor]

I hate centre thwarts. I prefer a walk-through boat without all that lifting legs to pass thwarts, mainsheet tracks etc.

It's not really a rower being 17 ft heavy and with a decent freeboard it would need a couple of oarsmen with long sweeps to make any progress.
Also the mast is stepped on the forward edge of the centreboard case and the centreboard mechanism would be a touch uncomfortable to straddle.

I've about decided how I am doing it and have just costed the grp materials and ply. Gulp. If it wasn't for the risk of paddling about in any collected water I'd almost go for using the hull as the floor.

 

[Avocet]

I've about decided how I am doing it and have just costed the grp materials and ply. Gulp. If it wasn't for the risk of paddling about in any collected water I'd almost go for using the hull as the floor.

I wonder if this would be stiff enough for a deck?

http://www.ecfibreglasssupplies.co.uk/p-2151-nidaplast-25mm.aspx

I was thinking of using it for the dropsides on a trailer.

 

[Lakesailor]

You haven't lowered the costs with that suggestion

 

[fisherman]

I wonder if this would be stiff enough for a deck?

http://www.ecfibreglasssupplies.co.uk/p-2151-nidaplast-25mm.aspx

I was thinking of using it for the dropsides on a trailer.

See my post #39 'Nidaplast is your friend'...
It is flexible until you apply the first layer of grp. It is very light, takes to GRP better than ply, cares not about wet.....

 

[CreakyDecks]

I would definitely have a drain plug. A few days rain weighs a ton! It's far easier to pull the boat out of the water a little and then open a drain than it is to empty it any other (manual) way. It's a pity there is no access to the transom, because a drain plug anywhere else will be awkward.

 

[dancrane]

I would definitely have a drain plug. A few days rain weighs a ton! It's far easier to pull the boat out of the water a little and then open a drain than it is to empty it any other (manual) way.

Not that Lakey needs to be told...but if a boat may ever be open to rain, a drain plug is pretty critical...as is remembering to leave it open, assuming it's above the waterline.

I lately used ordinary mastic to seal my self-bailers because they leak terribly. Now that they're sealed, I have to spend ages making sure the cover won't leak a drip in rain.

I'm putting in drains from cockpit to transom - no small job - but the hull/bilge shape will still accumulate gallons unless she's carefully propped-up ashore, or planing bows-up.

 

[Lakesailor]

Ah but. The transom is higher than most of the hull so draining would not happen unless the boat was tilted on the trailer.

I have glassed in the existing drain hole as it was 38mm and larger than most regular drain plugs available. I may fit a standard size drain plug nearer the bilge pump pick-up so that it will drain when the boat is just stood on the trailer. The previous owner started drilling with a hole saw to allow a plug on the keel at the stern, However when he cut a 4" hole with a hole saw through the floor he found
a) he had mis-judged and cut through the side of the keel
b) the keel was full of foam.

Misjudged hole cut

slot glassed with Fibral (GRP paste with glass strands) and then csm over.

Now glassed over, and drain hole forward glassed in as well.

I cut a plug of grp from a sheet (trials car bonnet) and bonded it in the hole and then glassed over.

 

[dancrane]

Ah but. The transom is higher than most of the hull so draining would not happen unless the boat was tilted on the trailer.

Yep, same problem. In fact, I haven't had the Osp planing yet, so I'm not sure if she'll drain through the stern when she's bows-up. She wasn't designed with transom drains.

A bit silly really. By the time I've repaired the previous owner's butchery, fitted drains & deck-struts, filled the stern with pop bottles and rebuilt the bulwark, I might have much more easily just paid £150 for two new Elvstrom bailers. But hopefully my work will look fine, and for years I'll shake my head at the original design which didn't have rear drains.

...previous owner started drilling for a plug on the keel at the stern, however when he cut a 4" hole through the floor, found he had misjudged and cut through the side of the keel...

If only you had an additional photo, of his face at that moment.

 

[lw395]

Yep, same problem. In fact, I haven't had the Osp planing yet, so I'm not sure if she'll drain through the stern when she's bows-up. She wasn't designed with transom drains.

A bit silly really. By the time I've repaired the previous owner's butchery, fitted drains & deck-struts, filled the stern with pop bottles and rebuilt the bulwark, I might have much more easily just paid £150 for two new Elvstrom bailers. But hopefully my work will look fine, and for years I'll shake my head at the original design which didn't have rear drains.



...

Most dinghies will partly drain from swamped via transom drains, but unless there is a double floor coming nearly to the waterline, I don't think transom drains will get rid of say 3 or 4 inches of water in the bottom of the boat. You'd have to be going very fast with the weight a very long way aft to make the floor slope towards the transom with the transom dry.
Elvstrom bailers or some cheap substitute are the only alternative to a bucket and sponge.

 

[dancrane]

That's what I'm realising. But I'm inclined to credit the previous owner with at least some idea of the boat's angle and attitude in boisterous conditions...

...otherwise, why would he have cut large ugly holes in the transom, and sawn away the rear cockpit bulwark? Not that I want to find myself sailing in conditions which would have challenged the draining ability of the self-bailers, but I reckon that was the reasoning behind his ugly modification.

If I kept a boat like Lakey's afloat, I'd want an automatic sump-pump. Would a small rechargeable battery be sufficient, with a solar trickle-charger? Do they work during rain?

 

[lw395]

Transom drains work really well from swamped to 'water sloshing around but able to sail', provided you've got say a F4 or more to reach away on.
I wouldn't want a Merlin without both transom flaps and elvstroms.

 

[CreakyDecks]

I may fit a standard size drain plug nearer the bilge pump pick-up so that it will drain when the boat is just stood on the trailer.

That is all I meant. Let gravity do the work!