380: Saildrive Fairing / Skirt

[tardis]

Appreciate info on replacement of the rubber/plastic skirt that goes around the saildrive as it enters the hull. Is this a Lagoon or Volvo part or can it be self made? If so what is the material to use?

[Ex-Calif]

Originally Posted by tardis

Appreciate info on replacement of the rubber/plastic skirt that goes around the saildrive as it enters the hull. Is this a Lagoon or Volvo part or can it be self made? If so what is the material to use?

I made one from soft vinyl and contact cemented it on. It lasted a season on my 120s saildrive. Partly due to my poor installation but it was gonna deteriorate quick.

I bought an OEM rubber one from Marine Parts Express. Much better.

[belizesailor]

Unfortunately, I just went through the ridiculously expensive process of replacing mine (different boat, but probably same or similar configuration -- MS25S bear box with 120S drive).

On most Volvo saildrives there are two "skirts" if you will. One fits around the sail drive and is secured on the outside of the hull -- this is just a fairing flap -- not a bad idea, but you can live without it and they usually tear off after a season or two anyway. This one you could fabricate fairly easily from rubber sheet material.

The other, much sturdier and much more critical, forms a seal between the drive train and the hull -- this one is installed where the transmission mates with the sail drive lower unit. This one is called the "bellows". You can see the upper surface of this one from your engine room.

If it is the bellows you need to replace then, I would not recommend trying to fabricate it or its associated parts because a failure could be catastrophic. But, when you find out the prices you will think about the possibility again!

Take a look and see which model gear box/sail drive you have in place. You will need these to get exactly the right parts. Note: your Volvo distributor can pull all this up with just the serial numbers.

MarinePartsEurope.com has some of the best public accessible parts diagrams available. Links for the models I have below. These will give you a good idea of how it all fits together and you can almost certainly find your specific models there too. See item numbers 39 and 29 respectively in the diagrams below.

Volvo Penta Exploded view / schematic Upper Gear Unit Sail Boat Drive Unit MS25S, MS25SR MS25S-A, MS25SR-A - MarinePartsEurope.com

Volvo Penta Exploded view / schematic Lower Gear Unit Sail Boat Drive Unit MS25S, MS25SR, Spare Part Solution MS25S-A, MS25SR-A, 120S-A, 120S-B, 120S-D, 120S-E - MarinePartsEurope.com

The boat of course must be hauled and the engine shifted off its mounts a bit, the saildrive decoupled from the gear box and then removed, in order to do change the bellows.

I also have a copy of good article that describes how to change the bellows in detail. PM me and I will email it to you.

[tardis]

thanks for detailed reply guys. Luckily so far its just the outer/lower fairing flap so I will try and make one up out of rubber and find a suitable adhesive. Meanwhile will save up for the bellows down the track

[Jon Hacking]

Originally Posted by tardis

Appreciate info on replacement of the rubber/plastic skirt that goes around the saildrive as it enters the hull. Is this a Lagoon or Volvo part or can it be self made? If so what is the material to use?

Hi Tardis - And Welcome to Cruisers Forum! The rubber outer skirt can certainly be hand made, & made better than the factory part. The factory parts are only thin rubber & hug the leg, but engine vibration tears them apart. We made ours out of 6mm truck mud-flaps that do NOT touch the leg & they've lasted 6 years now & don't show any real problems.

We've posted instructions for 4 saildrive modifications (including this one) that you might want to consider implementing, under our Cruising Info section. The part on changing the clip holding the secondary seal doesn't apply to your Volvo Penta as I think you only have a single seal (Yanmars have 2) but the rest is applicable to both VP & Yanmar saildrives. Putting in an oil-header-tank to keep water from coming in past your shaft seals is easy & really a must-do for all saildrives, IMHO

[Ex-Calif]

Originally Posted by belizesailor

The other, much sturdier and much more critical, forms a seal between the drive train and the hull -- this one is installed where the transmission mates with the sail drive lower unit. This one is called the "bellows". You can see the upper surface of this one from your engine room.

If it is the bellows you need to replace then, I would not recommend trying to fabricate it or its associated parts because a failure could be catastrophic. But, when you find out the prices you will think about the possibility again!

<snip>

I also have a copy of good article that describes how to change the bellows in detail. PM me and I will email it to you.

I am sure it is boat specific but I have always wondered if the standard running configuration (weight) puts the bellows above the waterline. From the lower "flap" there is about 8 inches vertical to the bottom of the bellows.

It would seem smart design to put the bellows above the waterline if possible. Then the bellows is more of a splash guard.

+1 on making the bellows hardware. Certainly can be done but I wouldn't try it.

PS - PM sent. Would love to have a copy of your article.

[belizesailor]

Originally Posted by Ex-Calif

I am sure it is boat specific but I have always wondered if the standard running configuration (weight) puts the bellows above the waterline. From the lower "flap" there is about 8 inches vertical to the bottom of the bellows.

It would seem smart design to put the bellows above the waterline if possible. Then the bellows is more of a splash guard.

+1 on making the bellows hardware. Certainly can be done but I wouldn't try it.

PS - PM sent. Would love to have a copy of your article.

On all the cats I have run, the bellows is definitely below the water line, but not all that far. If it is thought out well, and the engine room has a water tight bulkhead, then a failure could just flood this area and not even rise above the engine electronics -- I've seen this happen on an FP before, but fortunately have not had the opportunity to test it on any others.

Article copy sent to your email.

[Ex-Calif]

Originally Posted by belizesailor

On all the cats I have run, the bellows is definitely below the water line, but not all that far. If it is thought out well, and the engine room has a water tight bulkhead, then a failure could just flood this area and not even rise above the engine electronics -- I've seen this happen on an FP before, but fortunately have not had the opportunity to test it on any others.

Article copy sent to your email.

Many thanks.

Lets see - get a long stretch of surgical tubing. Stick it over the side and fill it. Cap it / plug it at one end. Haul that end over the side and place level with the bellows inside. Uncap it. Water flows = below waterline. Water recedes up the tube = above waterline - right?

I am too lazy of course...

[Jon Hacking]

Originally Posted by Ex-Calif

I am sure it is boat specific but I have always wondered if the standard running configuration (weight) puts the bellows above the waterline. From the lower "flap" there is about 8 inches vertical to the bottom of the bellows. It would seem smart design to put the bellows above the waterline if possible. Then the bellows is more of a splash guard.,.

Hi Calif->Sing - You're right that it would make sense, but the bellows (main seal) is always below waterline on all boats that I've seen.

In fact, the whole of the sail-drive is below waterline (to keep the engine weight low in the boat, I think) which is why the water on the outside is at a higher pressure than the oil on the inside of the SD. This means that if/when the shaft-seals go, salt water will enter & start turning your oil into mayonnaise, creating an emergency situation where you've got to haul the boat immediately to replace the shaft-seals.

That's why putting a header tank up high in your engine room (to raise the pressure of the oil to slightly higher than that of the water) makes so much sense. Then, when the shaft-seals go, the oil will start (slowly) leaking out instead of water leaking in. You'll see the level dropping in the header tank & know that you need to replace the shaft-seals the next time you haul, but it's no longer an emergency situation.

[Lagoon4us]

'Tis a great idea, i've done similar on the diffs of trucks that we had to use on the beach. At worst you will get a slow leak "outwards" which as Jon pointed out is an indicator....I'll be setting up same i like it. Cheers Frank

[colemj]

The Volvo saildrive is kept under a slight internal pressure by design. This works similar to the header tank to keep water out. Whenever I remove the dipstick, there is a whoosh of air escaping. Running the drive briefly again rebuilds the pressure.

The outer skirt needs to be mechanically fastened. I have not seen one yet that has stayed in place more than a few months using Volvo's glue kit and instructions. The best thing to do is make a thin sheet of fiberglass, cut it to size and screw it on over the rubber skirt. The fiberglass provides the hull fairing and the skirt keeps critters from growing inside the leg cavity. Our skirt is 14yrs old, hugs the drive leg and has no tears or other wear from the leg vibrating or moving.

Mark

[tardis]

Seems like the original design lacked staying power. A simple solution may be to make up the rubber fairing and not bother too much about adhesive but to use say 4 strips of Stainless steel and screw these around the outer edge of the rubber thus holding it to the hull. Hopefully there will be no issue with the thickness of the hull at this point or damage due to use of screws. Any comments?

[timbenner]

I used thin PVC sheets cut to size, with the Yanmar rubber seal glued to the PVC sheet material. I think that the Yanmar rubber seal that fits tight to the Saildrive and glued to the fairing plate is important to stop the water from flowing up into the Saildrive cavity. This should minimize critter growth up there.

I don't like the idea of screwing the fairing plate to the hull and it's not neccessary. I glue mine with lots of 5200 and wedge boards from the ground up to the plate to hold it until dry. Heat gun and paint scraper to get it off. I've been doing it this way for years and haven't had one come off yet - I don't like screwing into the hull, especially from under water.

[Island Sonata]

I have had both SD 20/30 sail drives on different boats an in both cases water through the shaft seals has leaked into the gear boxes . The very simple solution was to drill a pin hole through the top of the ridge on the yellow oil filler cap . What happens is pressure builds up in the gear box with long distance use an when you stop an gear box cools it goes on a vacuum sucking a small amount of water into the box even if the legs are brand new . By drilling a pin hole oil will not escape if gear box not over filled , pressure will not build up and a vacuum will not occur . Have seen many Yanmar owners do this in Australia curing the water in the gear box problem every time . Hull to leg rubber use incersion type rubber 6mm thick with Locktite rubber super glue it will not come off !! This rubber in Australia costs about $4.00 for a sheet 400x400mm / sheet .
Yanmar in their brief on their sail drives do not continuous rate the operation of their sail drive legs I have read in the manuals .

[Lagoon4us]

Sika flexed a sheet of fibreglass for the outside dummy cover but drilled a series of 5mm holes all around the sheets perimeter, this allows the Sika to key into the sheet.

The recess moulded into the bottom of a Lagoon does not match the OEM (Volvo) rubber moulded sheet.

In this picture you can see Mr Crab who went into the space when he was younger, this pic i took of the 'Black Pearl' in Georgetown 2 or so years ago.

Cheers