Mast step question

Mast step question-Need help!!

Boat is a Pearson 10M, 33', 12,500 lbs disp. Spar is oval aluminium 5"x8" section.

Mast step is steel and sits in bilge, held in place with 4 of the ss keel bolts.

Needless to say, the mast butt is beginning to corrode.

After exploring numerous options, I'm leaning towards building a glass reinforced 'platform' which I'll bond to the hull. The platform will be think (approx 2.25") enough to raise the steel mast step out of the bilge water.

Step is 8"x17"
Estimate total compression load is approx 9,000 lbs.

Question is: Do I need the compression strength of epoxy or can I use polyester? Also, same question re: reinforcement; cloth or roving?

Looking for adequate (not necessarily ultimate) strength and lowest cost.

TIA

Cheers,

MikeR

 

Mike,

I am assuming that you will take out the steel mast step, build the foundation, and put the mast step back in. The compression strength of epoxy vs. polyester is not important--doesn't even enter into the thinking. Either resin, on a purely strength basis, will work. What you have to consider is how tight is the area in which you are working--is it down deep in the bilge, or is it pretty accessible? The deeper in the bilge, the harder it is going to be to prepare the surface for the new laminate. You need to go in with a coarse grinder to really grind the surface well. The better the prep, the more easily you can use polyester. But epoxy has the best adhesion of all, no matter what. And in this high load area, I would use only epoxy.

As for glass, you will get a faster build up of thickness with fewer plies with woven roving than with cloth. Go with woven roving. Also, you can add stitch-mat in between each layer of roving which will also build up compression strength and thickness. Stitch mat is mat that is stitched together, not bonded with a binder. Be careful here--regular binder mat is suitable with polyester because the binder dissolves in the styrene of the resin. You can't use binder mat with epoxy because epoxy does not have any styrene in it, so the binder can't dissolve, it just makes a gluey mess in the layup. So the thing to remember is: with epoxy resin use stitch mat, and with polyester resin use binder mat.

Finally, it is not clear how you are going to build this step into place from your description, but I assume your total thickness makes your step a solid block on hull bottom, in other words, not a shelf with space underneath it. The step should indeed be solid to the hull. And for that thickness, you can also use plywood in the layup, encased in the epoxy fiberglass. So what I would do is use some fiberglass and epoxy first in a layer or two, add in 1" plywood, cover entirely with a few more layers of fiberglass and epoxy, add another 1" of plywood, and finish off with a few more layers of fiberglass and epoxy, encasing the whole assembly. That will be plenty solid.

I hope that helps.

Eric

 

Thanks Eric, pretty much echoed my thoughts. Bilge is very accessible and I've done previous glass work successfully. Happy to hear about the compression factors but will probably use epoxy anyway because of adhesion issues.

Anyone else?

Cheers,

MikeR

 

It would be cheaper to build a new step in SS or aluminum. However, if you want to take the heel of the mast higher, you could get an I-beam of SS, secure it to the existing four bolts and bolt the mast step to the top of it.

 

I'm with Gonzo

take out the old one, build a new one in stainless steel, bolt it back in.