Backing Plate Question

[Bob Perkins]

Hi Everyone,

I'm thinking it would be a good idea to have a backing plate for the prop strut. The strut has eight 5/16" Silicon Bronze screws that come up through the keel.

The bottom of the boat is 2" thick at that point - a plate is extra insurance I'm sure. But what material? I haven't found bronze plates available for drilling. I have some concern about dissimilar metals - but it will be a fresh water boat.

Should I just get stainless or aluminum and call it a day?

Thanks for your suggestions,
Bob

[Jack Heinlen]

I don't know where, but you have to be able to find some 1/4 or 3/8 bronze plate somewhere, and someone to cut and drill it for you. Take caution to secure the stock well if you decide to drill it on a home drill press. And bolts, obviously, if you do. Sounds like a good idea to me. I wouldn't mix metals here.

[John E Hardiman]

Remember to size the backing plate so that the bearing area of the plate x the compressive strength of the wood is greater than the tensile strength of the screws x number of screws. Otherwise you will crush the wood rather than hold the strut (and rip a hole in the hull rather than rip the strut off in a grounding).

[Thad]

Admiral Metals, 11 Forbes Rd, Woburn. Go south from 128 on Washington. Go 1/3 mile then left at the lights and immidiately right on Forbes Rd. Go to the end of the road into Admiral Metals. In the corner nearest the enterance is the retail outlet. They should have the plate there.

[Bob Perkins]

Whoo Hoo!

Thanks Thad - Nice and close for me smile.gif

Take Care,
Bob

[JimConlin]

On a boat where weight was a more acute concern, I'd consider G-10 glass-epoxy laminate for backing plates. It's a tad lighter than bronze, can be bonded in place and there's no question of dissimilar metals. 1/4" thickness costs about $24/ft^2 from McMaster-Carr (http://www.mcmaster.com/) catalog page 3346

[sdowney717]

My egg has backing plates for the struts. I thought this was normal. Each strut has 2 plates and are fit between the floors. They are 1/4 to 3/8 inch thick and look like brass. So they survived 35 years in ocean water and show no signs of corrosion. Someone used large steel washers on top of the plates and they completely rusted away. Any easy way to tell brass from bronze?
Is brass golden yellow and bronze always brownish?