Expandable Foam as Mast Wedge

[svHarbinger]

Two of my neighbors have gone the Spartite route with great success. The first one to bite the bullet has an all aluminum, cutter-rigged sloop. The second has a fiberglass yawl (plywood cored deck) with new aluminum masts.

In the case of the cutter I know the owner installed Spartite about four years ago and subsequently pulled the mast at haul out about two years ago. He had coated the mating surfaces w/ the recommended release agent and had absolutely no trouble removing or re-stepping the mast. The only snag he encountered was during the initial pour (which I witnessed) when some of the liquid Spartite escaped the dam he constructed and made quite a mess inside. I recall some rather vivid vocabulary accompanied that incident. Anyway, prompt cleanup erased all signs of the spill. I did, however, make a mental note to take care when constructing the dam to ensure a watertight barrier, particularly around the sail slide extrusion.

In the case of the yawl, the owner installed Spartite about four years ago and has had no issues since.

I am about due to pull my mast and when I do I will likely replace the rubber wedges with Spartite. It is expensive, but isn't done every day. I would consider a knock-off product from Grainger if I could be sure that the properties were identical, or nearly so (i.e., durometer, longevity, etc.). In most cases, though, I've found that it pays to go with a proven system. At the very least, with Spartite, a future owner or a shipyard worker will know what he has when he sees it, and the sticker, if used, will remove any doubt.

Would love to hear more detail about alternative systems... i.e., exactly which compound from the Grainger catalog was used and with what degree of success. Final note: I walked into our Grainger outlet in Seattle and established a cash account with no questions asked, so maybe they're less less stringent these days about requiring a corporate identity.

[osirissail]

>>I would consider a knock-off product from Grainger if I could be sure that the properties were identical, or nearly so (i.e., durometer, longevity, etc.).<<
You got that backwards - - Spartite is a knock-off of the products sold by WWGrainger. Well, neither are "knock-off" - they are the same source material. Spartite is just repackaging the RTV that is also sold by WWGrainger and multiplying the wholesale price based on offering a convenient way for you to get the product retail.

[svHarbinger]

>>You got that backwards - - Spartite is a knock-off of the products sold by WWGrainger. Well, neither are "knock-off" - they are the same source material. <<

OK, semantics. Branded vs. generic. We make this decision every day in the grocery store. MinuteMaid in quart containers is a branding of a wholesale commodity readily available to other packagers. We pay the premium because it's easily obtained and of a known and consistent quality. Same with Spartite. We know for sure that it works perfectly in place of mast wedges. This doesn't mean one of Grainger's 69 RTV product SKUs isn't identical. It only means we have to do our homework to ensure we're not comparing apples to oranges. That homework has a cost, so I'm still wondering which SKU in the Grainger catalog fits the bill and how we verify that its properties are identical to Spartite's? I'd consider the generic, but not if I have to set up a testing lab in my back yard!

Incidentally, just found this anecdotal posting that suggests Spartite might not reign supreme in all conditions:

Excerpted from Cabo Rico 34 Gear & Maintenance

We are disappointed with the results of the Spartite mast seal/partner replacement. The polymer material seems like a great idea and probably works fine in areas where there is a more moderate annual temperature range. However, my assumption is that the expension and contraction of the aluminum mast has caused the Spartite to move a bit due to mast length contraction in extreme cold northern temperatures. This has created a gap of 1/8"-1/4" between the Spartite and the top of the mast collar. I guess I will have to grind the stuff off and go back to the conventional partners. I need to rebed the collar anyway and the spartite prevents that as well unless the mast is removed.

[osirissail]

Originally Posted by sneuman

Wondering if anyone has ever tried this. To me it seems idea, as the stuff form fits and is solid as a rock once cured.
Thoughts?
I am talking about the stuff in a can you can get from Home Depot, etc.

Wow, I think we really diverged from the original post's question. Spartite/RTV is not an expandable foam but rather a liquid that becomes a rubber-like semi-flexible solid system.
- - Household and industrial "expandable foams" do just as the name implies - foam up with gas to greatly increase their volume. They come in many varieties from low expansion "semi-structural" to really high foaming "flotation" foams. Unfortunately they become rigid after curing and any "shock" loading to them will deform/collapse them. They were typically used to fill voids in decks between FRG skins or in bilge/wall areas to close off pathways for water, etc.
- - The "foams" shrink or radically decompose in the presence of UV so must be used in areas hidden from sunlight. Heat will also shrink or decompose the foams. They were originally thought to be a great replacement for the rapidly disappearing sources of balsa for coring. But long term they did not hold up so now a "honey-coam" system using polyester resin cell walls has replaced foam. Good old balsa coring is still hanging in there.
- - Divinyl foam is used as a repair product for cored decks with sufficiently thick FRG skins to not put excessive pressure on the foam. Surf boards are made of the same type product but again have significant FRG skins to protect the interior foam from collapsing.
- - For use as a replacement for mast "partners," chocks, etc. expandable foam would absolutely not work as the mast will shock load the foam collapsing it, and for the other problems with UV, heat, and water/chemical intrusion.
- - RTV products are more resistant, have a measure of form recovery after shock loading and resistance to heat and water/chemical intrusion. But nothing is perfect as the post about extreme cold demonstrates. RTV/rubber products do not like extreme cold and get hard and brittle and have significant shrinkage. So in that case the old tried and true teak wedges still hold their own against all the "new-fangled" substitutes.
- - Using any RTV product for a mast requires that the cabin top be properly prepared to accept the poured liquid and then also absorb the loading caused by the mast's movements. I normally route out 3 inches of interior coring between the FRG skin layers and feed in a structural epoxy putty mixture to form a proper smooth bezel around the mast. The poured RTV mixture then becomes the "gasket" between the mast and cabin top. Properly done the mast will lift out cleanly without hanging up and damaging the cabin top. Additionally a metal "collar" for the mast boot that is around the mast hole is through bolted to a backing collar in the cabin to anchor the cabin top skin and epoxy support system inside.