Replace saildrive gasket with foam

[CarpeDiem 11]

I have heard of some people who replace the outside sail drive gasket with a foam insert and then glass over it leaving a gap which is filled with a sikaflex. 

Has anyone had experience with this? Type of foam? Size of gap? 

I had to remove my gasket and I am contemplating a new volvo gasket or the foam/glass option... 

Thanks 

 

[Island Time 746]

Why would you do that? The fairing cover on the hull side is easy to do. A Saildrive is engineered to be able to move significantly via the engine mount flex, some in use, more in an impact. This movement is extended at the base of the saildrive where it protrudes through the hull. Filling the void will load the SD in a manner for which it was not designed. It will also make removal of the drive for any service work much more difficult.

[Frank 18]

I have a Volvo SD and I agree with IT,  also I'm sure you will transmit vibration to the hull negating one of the benefits of an SD. The fairing boots are not particularly expensive so I'm curious as to why you would contemplate this ?

 

 

[CarpeDiem 11]

The decision/investigation stemmed from three independent conversations.

Yesterday my antifoul painter said that a lot of times he is finding the boot is replaced with foam. 

Independently, last week my engine installer, when I told him I was replacing the boot, said he'd just done an new SD installation and the owner had a builder cut foam inserts claiming it was superior to the boot and he's been doing that for years.

And when I told someone else about the boot in the a conversation about inspecting the rudder bearings, he said 'well hell, if you've got a builder coming down, get him to replace the saildrive boot with foam. 

There is a limited number of posts on the Internet about doing this. It seems that alot of people have issues with the boot falling off personally I have never had that. But I do find that the boot becomes very chunky and lumpy and is not a smooth surface anymore. 

This is the most detailed I have found, this post was from 2014 and the op had the foam in since 2006.

https://www.myhanse.com/sail-drive-diaphragm_topic8671_page2.html

 

[Tamure 348]

I cant see a problem, on impact ( if the SD is hit you're in a heavy situation!) foam will crush. How much movement in daily operation cant be much, just fwd/rev thrust and vibration, it would be millimeters. Just thinking about it without  serious investigation, I'd  get some reasonably dense corecell and fit it in 2 halves around the SD with a large gap for the sealant say 20mm? 5200 is probably the right sealant but, Id use it to glue the whole thing in and when its all done fair it nicely  a bit of interprotect and see ya later!  

[CarpeDiem 11]

Boatright at Pier 21 said that they are doing this frequently. Quote: "Lots of race boats are having it done and we're seeing more and more cruisers asking for it."

They use a construction foam to fill the gap to about 20mm and fill the rest with sealant. If you need to take it out for any reason "stick a wire hook up there and yank."

With the lockdown I wasn't able to be around to watch, get in the way and be an annoying customer. But I got a couple of photos in the evening.

I believe the foam is about 2.5cm thick.

I will post another photo when she's next out at the Floating Dock. 

 

[Fogg 165]

This sounds like you’re on the receiving end of some dubious tech advice. A bit like the wide boys who think they can do a better job of redesigning their car suspension in their driveway than the manufacturers with their $millions R&D budgets.

I was always a bit unsure on the strength of a SD boot until one day - to my horror - the haulout crew accidentally lifted one of my previous boats out of the water with the rear lifting strop positioned under the bottom of the SD leg (skeg). It was inspected and found to be fine even after lifting half the weight of the boat. That convinced me the standard manufacturer’s design is OK.

[CarpeDiem 11]

11 minutes ago, Aleana said:

I was always a bit unsure on the strength of a SD boot until one day - to my horror - the haulout crew accidentally lifted one of my previous boats out of the water with the rear lifting strop positioned under the bottom of the SD leg (skeg). It was inspected and found to be fine even after lifting half the weight of the boat. That convinced me the standard manufacturer’s design is OK.

I suspect that would be the inside gasket and more importantly the engine mounts. Unless your engine was wobbling around with no mounts attaching it to the boat? I would not have expected any load on the inside gasket at all, unless a mount gave way? 

The outside boot slips down easily over the saildrive, so a sail drive going up into the boat (with no engine mounts to stop it) would just rise out of it.

[Fogg 165]

True. Although there was undoubtedly a decent load delivered to both the boot and gasket as the mounts moved to their extreme positions to absorb a few tons load.

[Island Time 746]

I had the same issue, but it broke a mount, and tore the seal. Also distorted the SD leg. Had to change the whole unit....