Fresh Water Mahogany

[IrishShores]

New to wooden boats, I am in the midst of purchasing a 1939 Royal Navy surfboat that has been converted to a gaff cutter. It is mahogany on oak. The hull is double-skinned: the inner skin is diagonal planking, the outer is carvel on oak stringers.
My question is fresh water. This boat has been sailed on the coasts of England and Ireland and if I buy it I will be bringing it onto Lough Derg, one of Ireland's largest inland (freshwater) lakes.
I read a terrifying paragraph about mahogany in an International Paint booklet: "Will last for many years in a marine environment with little protection as the seawater has antispetic qualitties. The same is not true with regard to fresh water, which will lead to rot and decay if allowed to permeate the wood fibre. Mahogany should, therefore be protected from freshwater at all times . . ."
Now, am I totally screwing up or can I "protect" it enough? If so, is bottom paint enough or should I try to put some kind of extra sealing layer on first?
I would really appreciate any real life experiences with mahogany planked boats in freshe water.

[Roger Cumming]

If you think about it, boats made of wood have sailed the world's lakes and oceans since prehistory. Salt water helps wood resist some kinds of deterioration, but encourages others such as worms and borers that only live in salt water. Fresh water in the form of rain does much damage to boats on both oceans and lakes. Coating wood generally helps reduce deterioration, as does ventilation and protection from direct sunlight. Mahogany is a durable boatbuilding wood which will last longer if painted, varnished or oiled. Find out how others protect their wooden boats in the lake where you intend to sail. Yearly maintenance will be necessary but will not be onerous if the boat is in reasonably good condition to begin with. One of the advantages of a wooden boat is that any part of it can be replaced if necessary by simply finding the appropriate lumber and someone with the skill to fashion the new part. Many wooden boat owners develop this skill themselves. The way to gain knowledge and experience in this is simply to begin doing it.

[Jack Heinlen]

Hi,

Owners of mahogany craft on the inland lakes of NA will be suprised to find that their craft rotted away fifty years ago.

It's a complex topic: what sort of mahogany, design, construction etc. The bottoms of some double-planked boats don't fare well in fresh water -- past fifty years. But as said the most pernicious matter is rot in the topsides due to rain, and that happens everywhere.

The most common fungus that causes rot doesn't grow in a salty environment, so a boat with its keel in fresh water has potential for rot all around. But, the rot only grows in a very specific moisture range(escapes at the moment, but its a 10 point range hovering around 20%) So, if the bottom is soaked(well past the range) and the topsides, deck, cabin and such are well sealed, no rot.

Say some more, ask questions, but relax about your boat simply dissolving in fresh water. It won't.

[ 04-14-2004, 12:51 AM: Message edited by: Jack Heinlen ]

[Dave Hadfield]

The cabin sides of my 1950 ketch are mahogany and the boat has never seen salt water.

But there has been rot. I had a large repair last spring of the cabin roof and part of one cabin side. As was said, keep the wood totally wet, or totally dry.

Make sure the deck and hatches and hardware allow no water into the edge grain of the wood at all.

[Noah]

There are a number of mahagony hulls that have lived their whole lives on my lake. These are both large and small boats, and have been here well over 50 years, so I wouldn't worry about it too much.

Noah

[IrishShores]

Thanks to all. I am much encouraged from these responses and from this site in general. I have to admit that the chance to own a 1939, wooden, double-ended cutter rigged sailboat is overwhelming!! I expect we will be able to get together on the price in the next few days and I'm sure I will be drilling, sanding and sawing soon after!!

[True Love]

Irish - Welcome! We'd love to see pics of your boat, so if you get a chance, don't be shy about posting them. If you need help doing so, we can send you the "how to's" for the WBF.