Help Please on two questions about Seacocks

[MV-Romnya]

Thanks Sailing_Jack, not sure how thick the hull is, I'd say at least 1/2 inch to 3/4 inch because it is an old sturdy boat - but will have a backing plate on stanby - will wait for someone with old boat know-how - MVR

[Stumble]

Rom,

Through hulls should always have backing plates, even in the hull thickness is sufficient structurally. They help to distribute loads over a larger area and properly are made from much stiffer material that fiberglass. Typically G-10 or metal.

Failing to use one can lead to localized crushing of the fiberglass, that down the line acts as a pass through for water to enter the hull.

[MV-Romnya]

Thanks Stumble, It must the wee hours in the morning over there - it's a beautiful sunny day here in Melbourne. What if the hull was wood - does it still need a backing plate ? - MVR

[Stumble]

Anytime you are through bolting you need a someway to distribute the load. For bolts typically you use a washer, for higher loads you use backing plates and washers.

Wood is great at a lot of things, but not at resisting the type of loads from through hulls. First you have localized compression across the grain that can lead to localized deformation. Secondly you have minute shifting of the bolts that over time can damage the wood, particularly if using bolts and not studs (only threaded at the very end).

Backing plates help minimize both of these problems. The localized compression issues by spreading the load. And the movement issues by, we'll spreading the load. And for very minimal cost. Figure a few dollars in parts and a few minutes in labor. To me it just seems shortsighted not to use them.

Btw it's only 6:40pm here.... So no worries.

[MV-Romnya]

Thanks Greg, great advice on the engineering of stress on wood - will do as you say - forgot you are on the other side and it is yesterday to us - it is 0947 here and 18c - Karl R

[MV-Romnya]

Thanks Sailing_Jack, I've checked out all the web sites re boat fitting in OZ and nothing - may have to order it in from your part of the world - only trouble is that shipping costs more than the product - MVR

[HopCar]

MVR following is a photo of the correct way to make a low profile thruhull connection.
The hardware you need is a Thruhull Fitting, Groco Flanged Adapter, Street Elbow and Ball Valve. Not shown are the backing plate or fasteners for the flange. With this setup there are no mis-matched threads. An improvement would be to put a support block under the ball valve.
If you can't find what you need in Australia, I'll be glad to quote you on what ever you need. I ship to Au often. Shipping costs aren't too bad when we use Priority Mail International.
Here is a link to my website showing the flanged adapter: Groco Flanged Adapter IBVF