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Old 03-02-2008, 09:19   #1
DWT
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Saildrive Boot

Saildrive Boot:

We hope to be purchasing a used 44' or 45'cat within the next year, and wishing for no more than two years. Having been a outboard and sterndrive mech. in my previous life I know the ups and downfalls of lower units. I would prefer a shaftdrive vs. saildrive but seeing what is out there forsale, I will most likely end up with a saildrive.

The newer saildrives have improved some, allowing you to change the oil without hauling the boat.....a good thing, more efficient than shaftdrives, and more compact but, my old training keep me on the edge. At lest I know or could figure out how to fix them myself if needed.

So to my point: With daggerboard, and I would like my new/used cat with them, this leaves those saildrive sticking right out there. If by chance someone did hit something how much of a WHAM, BHAM will that rubber boot around the saildrive take before she opens up to the sea?

And if just such a thing did happen...well, how does one cope with trying to plug up that now huge hole in the bottom you boat with a partial saildrive sticking out of it?

Has anyone out there have this happen to them or do you know someone?


David
69 Morgan 30'
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Old 03-02-2008, 10:10   #2
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Quote:
If by chance someone did hit something how much of a WHAM, BHAM will that rubber boot around the saildrive take before she opens up to the sea?
If you have through no common set of circumstances got yourself into that shallow of water I think there are a lot of other potential dangers as bad or worse. If you have crashed down on top of a rock using the bulk of the boat concentrated at one point then it won't matter if there is sail drive there or not. I think to rupture the hull would require that kind of force. The same might be said of an ordinary through hull fitting. Any large force concentrated enough might puncture the boat is an assupmtion we can not overcome.

I think there might be a lot of debate on the merits of sail drive vs. straight drive but I'm not so sure this would be part of it. Either could be damaged in a hard grounding and either might cause a rupture of the hull. The repair would likely be substantial in both cases. The difference between them in a narrow set of circumstances is a difficult scenario to predict.
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Old 03-02-2008, 13:16   #3
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Hi David - I have a boarded cat with saildrives.

Quote:
Originally Posted by DWT View Post
If by chance someone did hit something how much of a WHAM, BHAM will that rubber boot around the saildrive take before she opens up to the sea?
Hard to say, but it's seems plausible such a thing could happen. Perhaps this is one of the downsides to saildrives not protected by a keel and, thus, perhaps an advantage of minikeels over daggerboards. But neither are accident proof.

I believe the boot does not provide any structual strength. The WHAM, BHAM would have to be sufficient to fail the sail drive-to-transmission-to-engine mountings, then allow enough movement to dislodge the boot to allow seawater flooding. I don't know how much movement this would take.

But before that, in order for the drives to hit something, the "something" has to get past the bows and the deepest part of the hull (thinking of a floating log here - not the bottom or a coral head). On my boat, the deepest hull section is deeper than the drives. If the boards happen to be down at the time, perhaps they'll take the hit and shield the drives. But if the hypothetical log gets past the bows with boards up, it stands to reason that it could hit the drives, just riding along the hull bottom. In this case, maybe the drives will take one for the team and protect the rudders.

In the end, I can sleep at night knowing that if such a thing happens, my isolated engine compartments will only flood a little deeper than the normal water line.

Dave
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Old 03-02-2008, 13:27   #4
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Paul,
I was thinking more on the line of sailing along 6 or 7 knots and WHAM...hitting a log or something floating. The object than runs down under one of the hulls and hits the saildrive.
What does it take to open that rubber boot up? Maybe there is a one in a million chances that this may accure and if so someone tell me.
If I remember right there are 3 motor mounts and the force would have to be enough to break one or more to move the saildrive far enough to open that boot up.

David
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Old 03-02-2008, 13:36   #5
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Dave

You got in here as I was answering Paul. I see we both were thinking of a log.

I am looking for a Catana, a 43 footer. It is nice to know that the engine compartment is sealed or water tight from the rest of the boat....I did not know that.

My thought were if that boot let go it would flood the rest of the hull.

David
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Old 03-02-2008, 14:34   #6
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My thought were if that boot let go it would flood the rest of the hull.
Not on cats with isolated engine compartments, like the 431. I estimate that on my 471, engine room flooding would result in about 10" of water up against the forward bulkhead (the deepest part). There's also a watertight crash box aft of the engine room that the rudder posts pass through - ripping off a rudder post would flood only that small compartment (to a few inches). BTW, the rudders are the deepest part of the boat - substantially deeper than the saildrives.

Dave
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Old 04-02-2008, 11:28   #7
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We are the distrubutors for Lombardini in South Africa and we keep the ruber flanges in stock, 2 reasons for them to burst so far
1 lifting the boat and misjudging where the lifting point is and by accident having the strap sit over the sail drive , twice last year.
2 hitting something with a very high speed and I mean above 8 or 9 knots once last year.
there are a couple of hundred of these motors in service here.
I feel if you change these rubber flamges once every 5 years the chance of one bursting is minimal
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Old 04-02-2008, 12:20   #8
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On my Yanmar saildrives, the rubber boot is strictly a fairing device and is NOT even watertight. Now, the actual rubber diaphragm is further up inside. There is also quite bit of 'give' to the assembly.

Hitting objects is never a 'good' thing. It's all part of the risk of boating. Even a fixed shaft can have a strut bent which might even violate hull integrity. For me, it ended up being one of the compromises I had to make to get the other things more important to me.
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Old 04-02-2008, 12:56   #9
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since you have yanmar saildrives you have dual diaphrams and a warning light to come on if the outer one is leaking. I think that is a good extra safety feature. he outer fairing device we cannot keep on our cats , however good we gleu or silicone them on after some sailing they are always loose and come of totally. we now make a insert in the mould so they sit recessed and that works better
we also fill up the hole around the leg with a high density polyurethane foam to keep the water out of there for a bit of gained lift.

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Old 04-02-2008, 13:08   #10
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Fastcat 435,

This is the first time I have heard of the dual diaphram and the warning light on the Yanmar saildrives.

Is this on just the new saildrives because some of the boat I am looking at are 12 to 13 years old.

David
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Old 04-02-2008, 13:45   #11
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For the outer fairing boot for my Volvo saildrive I have cut my own from a large tire innertube and glued it on with 3M5200 and it does seem to stay a little better but after 1 year the corners start to give way. Anyway it is alot cheaper than the OEM fairing boot and you can cut a few and always have them on hand for next to nothing. I like fastcat's idea too.
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Old 04-02-2008, 16:35   #12
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Yanmar has had dual boots for a few years. Volvo does not.

I'm not worried about floating debris. It would take a good bit of force to shove the drive up in the hull.
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Old 04-02-2008, 19:12   #13
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Quote:
Originally Posted by cchesley View Post
On my Yanmar saildrives, the rubber boot is strictly a fairing device and is NOT even watertight. Now, the actual rubber diaphragm is further up inside.
Same with my Volvo saildrives on my Wildcat. A few months back while diving on my boat I noticed that the portside boot had fallen off so I ended up tucking it up inside the hull until my next haul out which was today. Like ccesley has stated, the boot is not intended as a watertight seal but to help with the flow of water along the bottom of your hull where the saildrive protrudes. The circular gasket ring is secured with 12 bolts. I've attached a photo to reference. Has anyone had luck 5200 - ing a boot while in the water?
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Old 04-02-2008, 21:38   #14
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DWT.... My 22 year old Yanmar saildrive has 2 watertight diaphrams and a lower rubber boot. They still make them the same way today. I have a Yanmar saildrive SD20 on my keel boat that is 22 years old with the same
upper and lower diaphram. I check the upper one closely every month. There is a sensor that sets of a alarm if there is any water between the 2 rubber diaphrams.
The only time that alarm has gone off is when I remove it and dip it in a can of water to check that it is functioning properly. Diaphrams are robust and whenever I question the Yanmar dealer about changing them, he indicates there are somewhat older units than mine in the area that are still going strong. Over the years I have checked the internet and talked to fellow saildrive owners never have heard of failures from age. Yanmar still makes the SD20 22 years later with the same diaphrams.
The lower rubber boot (after much trial and error) will stay put with "boatlife life chaulk" says can be applied under water but I've only used when hauled and then let it dry good before launching.
Over the years I have run into my share of misplaced timbers and logs and the saildrive faired well but it was, at least partially, protected by the keel.
I hope this helps.

Hugo
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Old 05-02-2008, 05:31   #15
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DWT...The lower rubber boot (after much trial and error) will stay put with "boatlife life caulk" says can be applied under water but I've only used when hauled and then let it dry good before launching...
Hugo
Polysulfide sealants, such as BoatLIFE'sLife Calk” or 3M's101", bond to wood, metals and fiberglass; however, they can melt some plastics and acrylics, such as Lexan, and some vinyls can become softened by exposure to their solvents.

Since polysulfides are a moisture/temperature cure, requiring the absorption of moisture from the surrounding atmosphere, an increase in the relative humidity or submersion in water will result in a shorter tack free time and faster cure.

"Life Caulk" takes a very long time to fully cure in air - up to two weeks, and "101" is somewhat quicker (but still slow).
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