Rub Rail Caulking?

Feb 14, 2014
5,714
Hunter 430 Waveland, MS
After searching the forum for "Do's and Don't" I found a lot of variation on caulking but was mainly on installation. Rub rail design is as varied as boat construction and size.
I am not even sure of how my boat deck hull is fastened and water proofed to the main hull.
RubRail.jpeg

You can see where water has passed behind the rubber rub rail. I have not located a drain point other than the under side. It appears either OEM or PO caulked the gap with now failed caulk. I am going to, at minimum, clean and flush and perhaps check for potential leaks.

Thinking out loud, I would think any caulk would have to adhere to rubber and hull, take an impact and flex, endure in a marine environment, and of course not look too ugly.

What are the forums recommendations?
Jim...
 
Jan 22, 2008
319
Hunter 29.5 Gloucester, VA
I did mine by cleaning all the old gunk out of the crack between the rub rail and hull. I used Acetone to clean down in there and then sealed with clear Lifecaulk. It stopped 90% of my interior leaks.
 
Feb 20, 2011
7,793
Island Packet 35 Tucson, AZ/San Carlos, MX
My only recommendation would be, if water's gonna get it, it needs a way to get out.
 
Mar 20, 2012
3,983
Cal 34-III, MacGregor 25 Salem, Oregon
if it were me doing it, I would remove the rubber and seal the deck joint... the rubber is really just a trim piece and NOT a seal, so caulking it is not going to be the correct answer....

sealing the deck joint under the rubber will be a much easier process for better looking and long term results using 5200.

then reapply the trim rubber to cover it all up...
 
Jun 19, 2004
360
Morgan M28 O/I Ocean Gate, NJ
FWIW, I agree with Centerline... the rubrail is not the seal. If you're interested check my posts on our Morgan 28OI, the Merry Bee. She has an outward- facing flange that is caulked and screwed. Old caulk was dried out and cracked leading to many leaks. We had to remove the rubber, dig out the epoxy caulk and reseal the joint with 5200. Life is good!:dancing::dancing:
 
Last edited:
Feb 14, 2014
5,714
Hunter 430 Waveland, MS
if it were me doing it, I would remove the rubber and seal the deck joint... the rubber is really just a trim piece and NOT a seal, so caulking it is not going to be the correct answer....

sealing the deck joint under the rubber will be a much easier process for better looking and long term results using 5200.

then reapply the trim rubber to cover it all up...
I have not found any leaks that I can point to the Deck/Hull seam, but perhaps I am kidding myself. I was hoping that someone knew how my boat or any Hunter of similar size or around 1998 production years, was "fitted" and "sealed". If I would have designed it, I could NOT flange it , but deck "lid" over hull, thus providing a water dam. Mechanical flanges tend to leak over years of stressing.

If no one knows for sure, then I will pull back a section of little used bumping and examine. I know that Hunter, in those years used 5200 for "everything screwed". So I don't expected a leak there.

I am looking at the polysulfide LifeCaulk, one part, and Polyurethane adhesive/caulk (this adheres better and more permanent)

I agree that caulking vs. sealing is not a cure for a leak, but may be a cure for water accumulation behind the rub rail.
Jim...

PS: Hoping not to remove the rail until I need a new bottom paint in 3 years.
 
Mar 20, 2012
3,983
Cal 34-III, MacGregor 25 Salem, Oregon
I have not found any leaks that I can point to the Deck/Hull seam, but perhaps I am kidding myself. I was hoping that someone knew how my boat or any Hunter of similar size or around 1998 production years, was "fitted" and "sealed". If I would have designed it, I could NOT flange it , but deck "lid" over hull, thus providing a water dam. Mechanical flanges tend to leak over years of stressing.

If no one knows for sure, then I will pull back a section of little used bumping and examine. I know that Hunter, in those years used 5200 for "everything screwed". So I don't expected a leak there.

I am looking at the polysulfide LifeCaulk, one part, and Polyurethane adhesive/caulk (this adheres better and more permanent)

I agree that caulking vs. sealing is not a cure for a leak, but may be a cure for water accumulation behind the rub rail.
Jim...

PS: Hoping not to remove the rail until I need a new bottom paint in 3 years.
I misunderstood.... i thought you had a leak you were trying to stopper up.
if you want to seal just the top edge of the rubber bumper strip (which is almost never recommended), then in my opinion the best product is the 3M 4000UV... its the most uv resistant and will look new for a long time....

I have done the same thing you are attempting many times, and it can help slow down a leaky hull joint, but what you never want to do is seal the bottom of the rail.... it may take a splashing at times, but any water that gets under the trim, NEEDS to be able to drain away....

to do a really nice job, clean the area to be caulked with lacquer thinner or acetone, VERY WELL.... then mask along both sides of the seam/crack, about 1/8" to 3/16" away from it, all the way around the boat...... then apply the caulking to the seam.... fair it down firmly (I prefer to use my bare finger so I can feel how its laying in), and apply a bit more if needed where the seam may be wider and taking more of the caulking into the void.... and make sure to fair it firmly and evenly...
then pull the tape before it starts to skin over......
then you can very gently, yet smoothly fair out any tape lines that may have been left.... WARNING, if you wait to long to pull the tape and and the caulking skins over, the tape lines may be a bit harder to fair out with a gentle hand..... but it can still be made to look like a professional did it, but with somewhat more effort...
 
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Feb 14, 2014
5,714
Hunter 430 Waveland, MS
then in my opinion the best product is the 3M 4000UV
I just looked up all alternatives on West Marine Advisor
http://www.westmarine.com/WestAdvisor/How-to-Select-Sealants-and-Caulk
I am partial to Polyurethane, which is my landlubber preferred sealant/caulk for it freeze/thaw properties.
All 3 types meet the compatibility tests for rubber to gel coat and stays flexible. The LifeCaulk has poor adhesive properties.
clean the area to be caulked with lacquer thinner or acetone
I never bring acetone on my boat, to inflammable for me. The 4000UV specs say Mineral spirits or kerosene
or
3MTM General Purpose Adhesive Cleaner ( it is too general purpose for my liking)
http://multimedia.3m.com/mws/mediawebserver?mwsId=SSSSSuUn_zu8l00x4xt9PxmxOv70k17zHvu9lxtD7SSSSSS--
West Marine has a description error calling it polyurethane type.

From 3M...
http://multimedia.3m.com/mws/media/...alant-fast-cure-4000-uv-05280-06580-06586.pdf
@centerline Great choice! I like your esthetics style too. Plus a drainage path is also needed for sure.:thumbup:

I still want to peek underneath the rub rail unless someone has done it already for this big Hunter boat.:pray:

Ordering some 4000 UV today.
Thanks...
Jim...

PS: It look like it might bond too well.o_O
 
Feb 14, 2014
5,714
Hunter 430 Waveland, MS
top edge of the rubber bumper strip (which is almost never recommended),
After inspecting the my entire top side of the rub rail, I found only 2 drainage "ditches" for my deck. The port and starboard deck drains ( 14" wide) are probably the only significant water flows over the rub rail. I now believe the PO was looking for a mysterious leak ( I found the stanchion support bolt in the same area as the drip source). He must have added the LifeCaulk ( I found the 2 partially used tubes in his parts box and the old caulking shown in my Picture).

So...

@centerline thanks so much, your insight has been my guide. I will use the LifeCaulk to seal the ditches about 2' , leaving a tiny mound at each end ( tiny dams) to force the drainage ditch water overboard and not flow left/right.

I picked LifeCaulk from its low adhesive properties, so I can remove it, after this season if necessary. I plan to flush/clean the algae and inspect for obvious leaking.
Thanks again to all who responded.
Jim...
 
Mar 20, 2012
3,983
Cal 34-III, MacGregor 25 Salem, Oregon
After inspecting the my entire top side of the rub rail, I found only 2 drainage "ditches" for my deck. The port and starboard deck drains ( 14" wide) are probably the only significant water flows over the rub rail. I now believe the PO was looking for a mysterious leak ( I found the stanchion support bolt in the same area as the drip source). He must have added the LifeCaulk ( I found the 2 partially used tubes in his parts box and the old caulking shown in my Picture).

So...

@centerline thanks so much, your insight has been my guide. I will use the LifeCaulk to seal the ditches about 2' , leaving a tiny mound at each end ( tiny dams) to force the drainage ditch water overboard and not flow left/right.

I picked LifeCaulk from its low adhesive properties, so I can remove it, after this season if necessary. I plan to flush/clean the algae and inspect for obvious leaking.
Thanks again to all who responded.
Jim...
Personally, I consider LifeCaulk a choice for short term repairs.... so it should work well in that application so you can see if it makes a difference, yet be able to easily remove, and try it a bit different til you get the results you want.
 
Jun 8, 2004
8,893
-na -NA Anywhere USA
Depending on the boat and year, underneath the rub rail generally is the hull to deck joint. Most manufacturers to include Hunter used 5200 to secure the hull to deck joints. You can remove that but if you do and find any of the 5200 bad, remove and replace. What you can do is put a seal of silicon of top of the rub rail but make sure it is pure silicon with no additives which will help to keep out the trash and many leaks if there are a few. There is a difference if the hull to deck joint were screwed together and finding that leak can be interesting. I just posted how to find leaks by pressuring the cabin and brushing with soapy water to air bubbling out.
 
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Feb 14, 2014
5,714
Hunter 430 Waveland, MS
underneath the rub rail generally is the hull to deck joint.
Do you know what kind of joint design? Hunter 430, mid range of production years.

Example:
1) Sandwiched flange. probably requiring vertical screws.
2) Deck over hull "lid" , like a shoe box lid. Probably requiring horizontal screws.

I am hoping style #2.
Thanks...
Jim...
 

Dan_Y

.
Oct 13, 2008
506
Hunter 36 Hampton
Jim
Our '08 looks to have a flat flange hull/deck joint with the rub rail fitted over the edge of the two flanges. It's not clear to me there are bolts through the joint either like our '91h30 had. Just lots of 5200 along "most" of the joint. The local dealer told me that hull/deck leaks were typical of this model. I just fixed one that I first thought was a leaking chain plate, but was the hull/deck joint behind the chain plate. Looked like the 5200 may have been missed or was very thin for an inch or two along that high stress area. Fix was to clean deep into the edges of the joint on the inside with acetone and some sand paper and caulk/fill the area with 5200 or life caulk per the dealer's recommendation. I used the latter because I had some on hand. I was fortunate to have access to that area from inside. Hunter made access easy for inspecting the chain plate hardware inside. I can see other water trails in various places along the hull interior that I'm sure are coming from the joint. My $99 Rigid bore scope showed stanchions and other deck penetrations to be dry around the chain plate, so the joint is my #1 suspect. The repair area has stayed dry for a month now in heavy rains. Now if I can just figure out how to reach the inaccessible spots.
Dan
 
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Feb 14, 2014
5,714
Hunter 430 Waveland, MS
Our '08 looks to have a flat flange hull/deck joint with the rub rail fitted over the edge of the two flanges.
Dang:frown:.
Easy to fit the hull and deck, easy to mold, and look ma' a place to attach rub rail.:biggrin:
Leaks? We aint worrin' about no stinkin leaks (for a least a few years ).

I looked for a spot to "peek" behind the rail. Nope that rail is not budging. The spring cleaning flushed and de-algae the top side. Looks much better. No apparent leaks inside. I will do post #9 this week and send follow up pictures.

Looked like the 5200 may have been missed or was :eek: for an inch or two along that high stress area
That is what happens, if you don't have a gasket between mating flange surfaces.:doh:
Thanks...
Jim...