Sealant for trim tab mounting?

[Brian1e]

Opinions on preferred sealant for mounting trim tab actuators below water line? Urethane i.e. 5200, 4200, or polysulfide? The PO used silicone sealant. One of the brass pipe nipples that pass through the transom split. A question I have is, could the silicone previously used contributed to this, corrosion stress? If so, I will pull the remaining three and re do them also. I am hesitant to use 5200, as I will have to disassemble at some point. Thoughts, suggestions? Thanks.

 

[Nomad Willy]

If you don’t use 5200 (probably best) I’d use SicaFlex bedding coumpound. I use lots of Sikaflex but below the WL on the hull I’d opt for 5200. I’ve not tried it but others here have said heat will break down 5200 for removal.

 

[koliver]

Whatever else you decide, NEVER use silicone. It is a guaranteed fail.

 

[Ken E.]

5200 is awful to remove after the fact but it is the gold standard for below the waterline.

 

[Keysdisease]

Contamination of the oil is a big concern with Bennett systems. They recommend fitting the nipple dry. If you call them (954) 427-1400 and tell them what you need they will send you a replacement no charge. Measure the nipple as there are different lengths. If you must, even though it says not to, Teflon tape is best, just be careful none of it gets on the first thread or two.

The female threads of the upper hinge can only tolerate being re-used once or twice, so proactively replacing the other nipples may not be recommended. They are easy (upper hinge of actuator) to replace and again, if you call Bennett they may send no charge. Ask for Thomas and tell him I sent you



https://bennetttrimtabs.com/wp-content/uploads/2015/02/ReplacementofActuator.pdf

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Remove actuator from transom and put pipe nipple into new actuator dry. Do not over tighten. Two to three[FONT=Minion Pro,Minion Pro][FONT=Minion Pro,Minion Pro] [/FONT][/FONT]turns past hand tight is adequate. Do not use Teflon tape.

 

[jleonard]

Use 5200. If you ever need to remove it can be done. Just heat a little with a hair dryer/heat gun.
I would use rectorseal for the hydraulic threads. Leave the first 2 threads dry. That will prevent contamination.

 

[Maerin]

Ditto the caution AGAINST silicone. It has very few righteous uses on board, certainly NEVER anywhere near the waterline. For the threaded connection, I've never been a fan of dry assembly, especially with re-assembled threads. I'd use Loctite 545 or other hydraulic sealer or Highside Leaklock, being careful to avoid the 1st 2 threads as others have recommended. I'm a big fan of Rectorseal #5, but not for oils, fuel or hydraulic. Leaklock or Loctite harden a bit and work better on small threads. NO TEFLON TAPE!

 

[Sugardog]

52 "McGoo" below, 4000 above. I know boats out there I built in the early 80's still not leaking passed 5200.

 

[Nomad Willy]

There’s no need to fear silicone.
It works very well on slick/smooth surfaces like glass and plastic.
But not to use it ever on a boat is slightly paranoid.

 

[diver dave]

Do not use 5200 on the item that passes thru the hull. Very difficult to remove including heat or debond. At most, use 4200. No need to glue this thing in.

As above, use PST for threads, avoiding the very end.

 

[koliver]

There’s no need to fear silicone.
It works very well on slick/smooth surfaces like glass and plastic.
But not to use it ever on a boat is slightly paranoid.

I may seem paranoid, but I am not wrong. I have seen silicone fails on glass frequently and on gelcoat it ALWAYS fails. Last time I looked, gelcoat was plastic. Silicone has absolutely NO PLACE on a boat. Nor is it wise to use it outdoors in any application where you might want a seal.

 

[Comodave]

If it was sealed with silicon, you need to really clean the surface to totally remove the silicone. I don’t know of any cleaners that will completely remove the silicone. Usually you have to scrape as much off as possible and then sand off the rest until water does not bead up on the surface. That is why most people do not use silicone. It can seal very well but it is almost impossible to remove well enough to let another sealant to stick.

 

[diver dave]

If it was sealed with silicon, you need to really clean the surface to totally remove the silicone. I don’t know of any cleaners that will completely remove the silicone. Usually you have to scrape as much off as possible ..

That's what my aunt had to do when replacing the space shuttle tiles.

 

[Brian1e]

Update: It appears that my identification of RTV silicone was incorrect. It appears that the previous sealant was 4200, or polysulfide. It cleaned up well, was semi-soft with a slight hydrocarbon odor.

I ended up using 5200 where the actuator attached to the transom, and where the bolts went through the mounting holes. I used 4200 from the inside to seal the pipe nipple through the transom.

Thanks for all the comments.

 

[Deano]

5200 for sealing trim to hull screws. Nothing on the actuator connections. IMHO.

 

[LarryM]

I would recommend 3M 4000 or 4200 on the mounting brackets because they both allow subsequent disassembly and are are recommended by 3M for use below the waterline. As for the hydraulic connections, here is what Bennett states in their Marine Trim Tab Installation Instructions:

Step 5 — Install the pipe nipples (dry) snugly into the actuator upper mounts. Do not use Teflon tape. Use care to avoid cross threading and do not over tighten (Turn in nipple finger tight, then two full turns with vise grips, NO MORE). Apply waterproof sealant on surface around pipe nipple and screw holes. Insert pipe nipples through transom and secure actuator upper mounts to transom with #14 x 1-1" screws. Note: Cover the ends of the pipe nipples with masking tape to prevent dirt or debris from entering the system. Remove masking tape before making connections inside the boat.

Step 7 — Inside the transom, apply Teflon tape on male threads of pipe nipples and tighten 90 degree brass elbows to pipe
nipples. While tightening elbow, hold pipe nipple with vise grips to prevent stripping actuator upper mount threads.

I suspect not using Teflon tape on the upper mounts might have something to do with their synthetic construction being joined to a metal nipple. They are pretty clear about it though.

 

[Keysdisease]

see post #5. The reason for the dry fit of the nipple into the upper hinge of the actuator is to avoid contamination of the fluid and has nothing to do with the dissimilar materials. The smallest oil passage in the Bennett system is in the valve seats of the pump and they are very small and prone to clogging with any contamination.

The reinforced nylon of the upper hinge and the thread sizing allow for a reliable dry fit and any sealant is unnecessary if installed per directions.

I suspect not using Teflon tape on the upper mounts might have something to do with their synthetic construction being joined to a metal nipple. They are pretty clear about it though.