Hull fairing around saildrive

Class rules require that you use the rubber ring, which is really an ugly thing. The normal method of attaching it is by marine grade silicon. Voila does not use a rubber ring and has used a removable fiberglass fairing to the area. If you send me your email address, I will post pics as I do not know how to do it on this site. My procedure can be done without removing the sail drive using the rotary extension cable to a standard Dremel tool and the metal rasp bit held in the end collet. It is better to use the extension cable because the thickness of the Dremel drive motor (main unit) will not allow you to get as close as you would like to the saildrive leg in order to present the cutting tool to the bottom of the boat at a 90 degree angle. Around the hole in the hull, place some masking tape about 5/8" from the hole and mask all the way around the hole to form your guide. With the Dremel, rout out a relief around the hole around 1/8" deep to create the recessed seat onto which your fiberglass fairing will fit. Oe could make this seat wider, but on my hull I run into some counter-sunk screws that fit through the hull and are buried in the gel coat, but you may find them if you go beyond 5/8" from the main hole.

Now lay up some fiberglass onto a flat surface separated with some waxed paper or other form of release until your lay-up is equal to the depth of your recess. I lay mine up slightly less, and then top it with some low density filler so that when I fit the pieces into place I can sand the seating surface until the finish surface is flush to the hull.

With some art board or some other type of material (shoebox cardboard will work) cut out the patterns that will fit into the recess and you may bring their edges up to within 1/8"-3/16" from the side of the saildrive leg. This would look like a miniture of the rubber ring. The inside hole of the rubber ring could be used to trace onto your patter to form the inside hole. This new oval ring must be cut into two pieces. Mine are cut at the center of the leading edge and the center of the trailing edge to facilitate getting them into place as a single piece will not slip over the bottom gear housing of the saildrive leg.

Trim your patter until it fits nicely into the seat. Now you can use the pattern to lay out the fiberglass fairing material. I advise cutting this to be slightly oversized, and then trim it down with some 80 grit paper on a sanding block, or use some other form. I trim the inside of the fairing with one of those little drum sanders that goes into a Dremel to get the inside to fit nicely around the leg. With this complete, again use your Dremel extension to hold a small drill bit so that you may now drill the holes into the newly made fairing fiberglass and into the hull. For this I temporarily fix the ring into place with a couple of dabs of silicon to stabilize it. I equally space bout 4 holes on each half. Additionally I do something with the front and back to join the two pieces together but that is more easy to explain in my photos. When the holes are drilled (these should be sized to be used as a guide hole for #4 counter-sinking flat head wood screws), remove the new fiberglass fairing plates so that you can now apply a counter-sink bit to the holes so that the screws will go in flush.

Please note that you must use an appropriate sized drill bit. Neither fiberglass nor kevlar will allow you to force a screw into a hole that is undersized and doing so will result in a broken screw.

If this job is done carefully, these plates can always be removed to facilitate removal of the saildrive and replaced. You may further refine this fairing by slipping either a large "O" ring around the sail drive, or some cheap packing rod from the local hardware store that is butt-end glued together. Slip this up the saildrive until it is just above the fairing, and then finger-in some marine silicon to fair the new fairing to the hull.

Want more refinement? Cut a little piece of the glass fairing and double up its thickness somewhere on the inside of the main hole well inside the seat ledge and drill a drain hole into it to be plugged with another screw. Now when you set the plates, seat them with a little bead of silicon around the seat and fair in the edges with the silicon. After you fair in the gap between the fairing and the silicon, you will have a water-tight compartment above the hull bottom and this will both reduce drag create several pounds of additional hull floatation.

Note: You will not be racing such a set up at the North Americans!

surface prep is everything.....

My solution to the rubber gasket was laying up several layers of fiberglass cloth on a flat surface (on wax paper) and then trim it to the size of the original gasket after curing.  This leaves you with a very thin lip on the hull after installation.  I've had good results using 3M Super Weatherstrip Adhesive for automobiles with both the rubber gasket and the fiberglass layup.  My racing has been strictly PHRF.

I hage an extra set of these plates and will photo them here at home tomorrow and then put them together with photos of the boat as prepped before mounting them and then email them to you tomorrow. Hope you and family had a good Thanksgiving.

Hi all.  I had the chance to replace the saildrive membrane on my boat last weekend (old one had fallen off when I hauled at end of last season!).  I thought I'd relate the experience here.  Thanks also to Bill who sent me some tips via email.

I purchased a new rubber membrane and the special glue from Crinmar.  I'm not sure what's so special about the glue because it smelled like any other solvent-based adhesive (smelled like model cement actually) but I didn't want to take chances.

Surface prep:  I followed the instructions from above with some slight differences.

First, I used a heat gun to heat the glue residue.  But rather than scraping, I used a cloth rag to rub off the warm glue residue.  I found this worked much better than a scraper.  Was way faster and no chance of gouging the fiberglass.

Then I sanded the remaining glue residue off to get down to bare gelcoat.  For this I used a 4" orbital sander on low speed.  I found 120 grit worked well.  150 would be OK. The trick is that a 4" sander is bigger than required, so some finesse is in order to make sure you don't sand more than is necessary.

Once you've got a nice clean surface, I wiped the surface and the underside of the rubber membrane with laquer thinner.  When installing the rubber membrane over the prop, be aware that there is a front and back to this thing with the opening being slightly wider at one end to allow for the tapered saildrive leg.

I pressed the membrane up against the hull exactly where it needed to go and outlined it with pencil, then dropped it back down again so it was resting on the prop shaft.

I then used a 1" metal putty knife to apply the glue to the hull everywhere inside the pencil line and also to the entire underside of the rubber membrane.  It was a pretty cool day and this stuff still seemed to be drying pretty quickly so I had to work pretty fast.

Lastly, press the membrane in place; using a rolling pin (or whatever you have handy) press firmly and roll from the inside of the membrane outwards, working the glue and any air pockets out.  I went around the whole perimeter a few times to be sure it was a nice tight fit.

Voila!  See pics of surface prep and the final product.  Just need to VC17 before launch.

https://goo.gl/photos/JaLZYwdbYQogwA8e6

Edited by Winner - 18 October 2016 at 9:01pm

yes. No problem.

John where did you acquire this new glue from?

no, for 4200 ,previous owner did this and it came apart, being a bitch to clean up. Used the Bostik and no problems since then.

Edited by bal149 - 10 May 2016 at 11:03pm

I'm launching in a couple of days and just noticed that part of my sail drive membrane us no longer adhered to the hull (about 1/8 of the entire membrane). I'm all out of the bostick glue. Anything else I can use in a pinch?

I use 3M Super Weatherstrip Adhesive for automobiles and have not had a problem.