E35 Mast plate

The am trying to get a new plate made to replace the one sealed within the fibreglass of the deck under the mast, which was seriously corroded when it came out. Clearly it is not something I want to have to replace again any time soon, since it involves dropping the mast and a lot of fibreglass work.

So far, I have had two suggestions, the first being monel, the second being galvanised steel. The cheapest quote I have had so far for monel has been $950 - several places originally said $300, but their sources for monel at that price never phoned back, as if the price has tripled in the last year. Galvanising would be a lot, lot cheaper. Stainless steel I have been warned would be weaker, and would not like the salt it would get from the four bolts holding the mast in place.

Anyone any thoughts on the longetivity of the different materials, bearing in mind where it will be going?

Gareth
Freyja E35 #241 1972

Gareth

Do you have a picture you could upload?


John

What are the measurements of this plate? Is it about a half inch thick?
Heck, for $900. I'll bet that I could make you a "plate" out of carbon fiber layers and epoxy... and turn a very nice profit... and it would be a lot stronger than steel!


Loren

My digital camera is under repair right now, so I can not put in a picture. The piece is approximately 12" by 8" by 5/16" (thickness is hard to be exact because of corrosion), with rounded corners so it can be glassed over. It has four screw holes for the base of the mast, and a large hole for the mast wires. The machining is nothing special, just the material if it is to last.

I know nothing at all about carbon fibre, except that it can be overstressed in speeds close to supersonic... do you think it might work for distributing the load of the mast?

Gareth
Freyja E35 #241 1972

"Plastics, my boy! Plastics" That's the future....

At 5/16" thickness, that plate is likely not transfering any loads except to keep the material under the spar from crushing. This would be similar to the use by many boat builders of marine plywood under their deck-stepped mast bases.
Water must have gotten into the old plate (and surrounding laminate) from water migrating around the holes for bolts and wiring chase.

I would think that a composite plate material would be better than wood or metal. Unless that plate were wide enough to be acting as a beam to carry a span load, a 5/16" plate of G10/FR4 epoxy glass material should be plenty sufficient.

McMasterCarr has this stuff in standard sizes, like 12" X 12" X 3/8", several resin colors (!), for $42.59.
http://www.mcmaster.com/
They call it "Grade G-10/FR4 Garolite"

Might be worth a phone call to them or email contact....

Or, for about $119./sheet, you could epoxy together a couple of these carbon fiber plates. Part Number: 86585K55

Food for thought!


Loren

That is right, the purpose of the piece is to spread the load of the mast over the deck core. I guess the mast load must be in the region of 10000 lbs under sail, not counting shock load. The original core at that point was strips of plywood, which were partially crushed. A book from the local hardware store listed pine as rated for 300 psi stress, I have some renicell E320 to replace it, which is rated for a 1000 psi stress. If 10000 lbs is spread over 80 square inches, that is 125psi, which gives a good safety factor.

So the plate must be able to absorb that kind of force, the web site you listed does not list many numbers for the material, but I will try to phone them.

There does not seem to be anywhere for the shock loads to be absorbed, I guess the compression post in the cabin will take them now.

Gareth
Freyja E35 #241 1972

flex or not

If the plate under the mast doesn't flex it will cause a stress point at the edge of the plate. The repair would crack would it not?

Strength is relative to the supporting area of the item. The plate must have compression strength to transfer the load to the compression post, the deck is not intended to support the load. Do you step bolts go into the compression post or just into the plate? If they depend on the plate then you would need to be sure that the material will hold the bolts.

Remember in the end wood lasted 30 years.

One of the differences between the E29 and E35 is the stepping of the mast. The plate I am talking about sits on top of the deck core, to spread the load of the mast onto the core (plywood), which takes the load on to the compression post.

I spoke to McMaster today, and one of their engineers told me that one 3/16" plate of 86585K55 would do the job. It would also take the thread taps for the mast base.

You raise a good point Randy - since I am talking about materials built to very high tolerances, it will be crucial to mate them together properly, to avoid problems at the edges.

Gareth
Freyja E35 #241 1972