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Author Topic:   mounting items on cockpit floor

adaco posted 07-12-2003 12:39 AM ET (US)
Given the various layers of construction, when mounting things like seats, cooler chocks and such in a Montauk, how deep into the cockpit floor should screws generally penetrate?
Tom W Clark posted 07-12-2003 02:21 AM ET (US)
adaco,
The screws should penetrate the full thickness of the plywood backing. If there is no plywood backing then you probably shouldn't be screwing anything there unless it very light weight.
Most of the small Whalers use 1/2" plywood as backing for mounting hardware and wood parts, but 1/4" plywood is also used as is 3/8" and 3/4" on the larger hulls. See the wood locating diagram for your particular hull to determine exactly what is where.
You can figure the fiberglass skin of the hull to be about 1/8" thick so add the thickness of the plywood and the fiberglass and the hardware being mounted and then use stainless steel sheet metal screws (NOT wood screws) equal to this length.
For example, if you were installing a battery hold down in the stern of a Montauk where there is 1/2" plywood, you would probably want to use a screw of no less than 3/4" length is the hold down itself were 1/8" thick at the screw hole (1/8" + 1/8" + 1/2" = 3/4").
It's perfectly fine for the screw tip of the screw to poke through the backing material and into the foam a small amount. Ideally you want the full diameter of the screw's shank and threads to be engaging the full thickness of the backing material for maximum strength.
Sheet metal screws have fully threaded shanks that are not tapered whereas wood screws have a tapered thread and shank which often has a smooth (unthreaded) shank below the head. Much less surface area of thread to engage the backing and thus far less strong. Generally, you will find that Whaler has only used sheet metal screws and not wood screws for hardware/wood attachment to the hull.

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Author	Topic: mounting items on cockpit floor
adaco	posted 07-12-2003 12:39 AM ET (US) Given the various layers of construction, when mounting things like seats, cooler chocks and such in a Montauk, how deep into the cockpit floor should screws generally penetrate?
Tom W Clark	posted 07-12-2003 02:21 AM ET (US) adaco, The screws should penetrate the full thickness of the plywood backing. If there is no plywood backing then you probably shouldn't be screwing anything there unless it very light weight. Most of the small Whalers use 1/2" plywood as backing for mounting hardware and wood parts, but 1/4" plywood is also used as is 3/8" and 3/4" on the larger hulls. See the wood locating diagram for your particular hull to determine exactly what is where. You can figure the fiberglass skin of the hull to be about 1/8" thick so add the thickness of the plywood and the fiberglass and the hardware being mounted and then use stainless steel sheet metal screws (NOT wood screws) equal to this length. For example, if you were installing a battery hold down in the stern of a Montauk where there is 1/2" plywood, you would probably want to use a screw of no less than 3/4" length is the hold down itself were 1/8" thick at the screw hole (1/8" + 1/8" + 1/2" = 3/4"). It's perfectly fine for the screw tip of the screw to poke through the backing material and into the foam a small amount. Ideally you want the full diameter of the screw's shank and threads to be engaging the full thickness of the backing material for maximum strength. Sheet metal screws have fully threaded shanks that are not tapered whereas wood screws have a tapered thread and shank which often has a smooth (unthreaded) shank below the head. Much less surface area of thread to engage the backing and thus far less strong. Generally, you will find that Whaler has only used sheet metal screws and not wood screws for hardware/wood attachment to the hull.