Thru Hulls

[Harold Anderson]

I will be changing to marelon thru hulls on my fuji sailboat. I don't want to drill any more holes in the hull to mount the seacocks. Can I just fiberglass the backing plates to the hull? What is a good material for backing plates other than plywood that can be fiberglassed in place? I plan on mounting the seacocks to the backing plates with bolts and nut plates. Suggestions?

[masalai]

Stick with the tried and true, it is simple, easy to observe/monitor and has stood the test of time... A friend has the suction end of his deck-wash system retracted into the chain locker of the anchor... It is pushed out through the drain hole when needed to wash the chain whilst hauling in the anchor... I have my water intake in the sail-drive legs of my boat and one outlet for the toilet-holding-tank below the water line... Outlet for the galley, shower and washing machine are all through the bridge-deck of my cat... The engine wet-exhaust pipes are just above the water-line... Engine exhaust, toilet and galley are all stainless steel fittings sealed with marine-grade "sikaflex" stuff... the others, being fairly well protected are plastic...

[Harold Anderson]

By tried and true you mean to stick with plywood? Is it ok to not drill the mounting holes thru the hull? Thanks

[Harold Anderson]

Is plywood the prefered material for thru hull backing plates? What other types of backing plates can be used. Must the seacock flange bolts be drilled thru the hull? Seems like a whole lot of new holes in the bottom of my boat! What bolts should be used to secure marelon thru hulls?

[masalai]

If your boat is made of ply, drill the hole with a hole saw, seal the exposed timber well, & if necessary add extra layers of ply & glass inside for greater stiffness, (I like to also add a woven tape of glass and fair the area both inside and out), then fit the stainless steel fitting with adequate sealant...

I am not a marine engineer or NA so get local qualified advice... I was advised to attach the seacocks directly to the thru-hull-fitting... don't forget to seal the thread too before tightening down...

[Harold Anderson]

Is plywood the material of choice for thru hull backing plates? What other materials can be used? Must the seacock bolts come thru the hull? Seems like a whole lotta holes below the waterline. What bolts should be used on marelon thru hulls? Thanks

[masalai]

What bolts? On a recreational grp/ply/DUFlex etc hull a threaded fitting is used

Here if a Bronze one http://www.mbms.ashop.com.au/p/54570...onze-13mm.html

and a bigger one http://www.mbms.ashop.com.au/p/54571...onze-50mm.html

The outside end is nearest and the flange threads down to secure the fitting in place... The seacock screws on to the thread after the nut/flange is brought home and seals the hole...

[Frosty]

The bolted plate thru hull is old stuff they don't do that any more, your thinking Tatanic.

Thru hulls are just a one hole one big nut tightening over the main body --Google it.

If you had some fibre glass lying around I would epoxy a 6 x6 inch peice to the hull.

Difficult when we dont know what your boat is built of.

[Landlubber]

Marelon is a tried and proven material, certainly for small craft. King Starboard is a good backing plate to use and seal it all down with FixTech (Polyurethene)

[masalai]

Thanks Landie, I knew someone would arrive sooner and settle the issue...

[Frosty]

This will all be usless when the poster says his boat is made of steel.

Can you weld Marelon?

[FMS]

I believe the Fugi 35 Ketch in his profile is a fiberglass boat. Please confirm Harold so there is no confusion.

[Steve W]

Harold, i use G10 (fiberglass/epoxy sheet) for backing plates,you can get it in all kinds of thicknesses. I buy it from Mcmaster-Carr. I have also mounted the Forespar seacocks the way you have suggested for the same reason, you can tap the G10, put a little wax on the ends of the screws and screw them in till they are flush on the bottom to keep the epoxy out of the holes,then glue the backing plates to the hull (of course proper prep first) and use machine screws to mount the seacock and then screw in the thru hull. If you use plywood use 3/4" BS1088 meranti or similar and make sure it is properly sealed with 3 coats of epoxy including the hole, ive seen way too many delamed backing plates.
Steve.

[Harold Anderson]

Thank you all for your ideas. I'm sorry that I forgot to say that my hull is made out of fiberglass. That was stupid of me. Thank you for the info and all the help

[Harold Anderson]

If Star Board was used for the thru hull backing plates can it be glued to the hull using West Epoxy? Can star board be threaded or will i need to install nuts or nutplates to the back? I want a backing material that won't rot.