B31 bottom blisters

[Amberjack]

During last year’s haulout Amberjack had a pretty good crop of small blisters and goes into the yard next month to deal with them. The boat will travel 35 miles up Admiralty Inlet to Port Townsend for this work because Seattle boatyards have become expensive. From reading the B31 forum over the years most Bertram owners who deal with this issue chose soda blasting, probably because the lifting strakes make it awkward for a microplane device. The yards up here are all talking microplanning and unfamiliar with soda blasting so I need information to be able to talk with them intelligently. Can any help me with the following questions?

• What are the merits of soda blasting vs microplaning? Is there a downside?
• How many hours should it take a professional to soda blast a B31 hull
• Are the through hulls and shafts removed for soda blasting as they are for microplaning
• Any other comments

I appreciate any input you can send.

[ranjr13]

We just had our 31 done in June/July - blasted, barrier coated, 1 marker coat of paint, then 2 coats of final color paint. The blasting was not soda, but actual sand blasting by someone who does that on a regular basis. They took it down leaving just enough color to sand down to the gel coat - came out awesome. The prep was almost as long as the blasting, have to do a tent from water line down to ground, cover ground, and tape/seal all through hulls and cutlass bearings. It took about 50 hours for all, prep, blasting, some very minor blister repair, barrier coating and painting. For just the professional's time on blasting, it took about 1/2 a day. I have no experience with microplaning - only used blasting on past few boats over the years, and very pleased with the results.

One other tip/concern - really try to do it with a completely dry hull. Ours was out of the water since last Fall. If you are running it and having it hauled to do, I'd try to wait as long as possible once on the hard to get any moisture out of compromised areas.

Best of luck.

Bob

[Pete Fallon]

Amberjack,
The soda blasting is less abrasive than regular sand blasting and it is less messy. I have had clients with blister problems on their boats and only had one boat get gel coat peeled, it's like a electric planner that takes off a little at a time. The 1973-74 Bertram's had the most problems with blistering due to the company experimenting with different suppliers of resin due to the first oil crisis back in 1973 when oil prices went up. The earlier boats 1961 to 1972 had only a very few blister \problems, I personally would not buy a 31 that wasn't built before 1972 because of the resin crisis.
The thru hulls don't have to be removed for Soda blasting, it's less abrasive to the laminate under the gel coat. A 31' Bertram should take less than 8 hours to blast the bottom and it can be done if it's raining . The best is to let the boat dry out for at least a month before doing either method.
Pete Fallon

[Tony Meola]

Doug

We did our 31 in 1986. Sand Blasted and 5 coats of interprotect. She is still good.

Let me say this, if you have blisters, I am not sure Soda blasting will open them up. Maybe someone who has had the soda blasting done, can let us know. I will tell you that Sand Blasting opens everything up. And I mean everything. Every void in the gel, pin holes etc. I spent days scouring over the hull filling in every single pin hole.

Interlux, also made an additional sealer that could be put over any bare glass that was exposed and not actually a void. For example an area that may of had thin layer of gel. Not sure they still use that sealer. We used all interlux products as that time, that was about all we could get our hands on. After it was balsted we did the rest ourselves, since the yards had no idea as what to do.

Now the key for us was that back in 86 we had a bunch of guys who fished inshore and offshore with us so we put them all to work. Had to have all 5 coats back then on in one day, or would have to sand between coats. Picture 6 people, including my wife who I was only engaged to at the time, taking a section and putting the interprotect on her.

Would I do it myself today, nope, too much work. Filling every void was a royal pain.

We followed Interlux's instructions to a T and I suspect that is why it held up so long. Only regret I have is that ablative paints were new to the market so we stayed hard paint, and not I use ablative but I have paint flaking off. The interprotect is still good though, and when it flackes, there is still a layer attached to the interprotect.

I believe if you check Interlux's website, they recommend getting the bottom blasted then letting her dry out good. The issue is this, even if you put her in a barn, if it is damp, she will still absorb moisture. Most yards set up heated areas to dry the bottom.

Good luck.

[mike ohlstein]

Did mine last fall with walnut hulls. Worked great.

This is the stuff to use after....


Interlux Watertite Epoxy Filler & Interlux InterProtect 2000E Epoxy Primer

http://www.jamestowndistributors.com/us ... rrier_coat

[Amberjack]

Thanks all, as usual excellent advice and freely shared. What an awesome forum!

My fingers are crossed these are blisters between coats rather than osmotic blisters as this is a 1969 hull supposedly fabricated with better resin. I'll let you know what happens.

[bob lico]

i have a april 14 1973 31 with no blisters .i sand blasted to old 1st coat of inter protect that was applied incorrectly over green mold and flake 2" dia. pieces that made the bottom looked like a leopard each year .so i sanded last cote and filled in two any irregularities with epoxy,and 50/50 high density filler with collidal silica. then 5 cote process of alternate color inter protect with bottom paint within 4 hours of last cote of inter protect . pulled the boat last week to remove wire line around prop. bottom job with water based bottom paint perfect!!!!!!!!!!!!!!

[Bertramp]

Hi there guys ...
Well the Bahia is now north.
We did notice some blisters and the plan is to address them over winter.
For you Long Island guys, who did you use for the sand/shell/soda blasting ?
The boat may winter right on the side yard of my house .... and I would like to have it done there
Thanks

[Amberjack]

Hey Steve--You write this just as Amberjack is ready to splash this Friday after 7 monthsout of the water! I learned more than I need to know about blisters over the winter and hope this is my one time deal.

It sounds as though you plan to park the Bahia to dry out the hull. The yard sandblasted my hull down to green glass, then we kept Amberjack under cover and the topsides wrapped with plastic to keep the cockpit and interior clean while the hull dried. A couple months later I noticed moisture between the topsides and the plastic wrap even though we had heat in the cabin and the bilges were dry. After doing more research on hull moisture it turns out that hulls breath from the inside as well as the outside (of course--there's no barrier coat on the inside!).

From now on when I park Amberjack for more than a few days I'll crack some of the deck hatches just to reduce humidity in the bilges.

[Tony Meola]

Steve

Amberjack is correct, the hulls absorb moisture above and below the water. However, if the bottom is down correctly, you really should not have an issue with the Bilge.

As I have posted before, we did ours back in 1986, 5 coats of Interprotect and the problem cured.

I realize everyone will have there thoughts, but unless the issue is really bad, no need to go down to green glass. We sand blasted ours, ugh would not do that again. Spent days trying to fill every little dam pin hole. It did open up the blisters and voids but I believe soda blasting will do the same thing.

Maybe if Raybo sees this he will comment on that. All the areas that opened to green glass, due to voids we had to put a special sealer on that area and it was recommended at that time by interprotect. I believe it 1001 and I am not sure they require it anymore.

If you having the bottom done over the summer and then letting her sit until the spring, then you need to think about keeping the bottom dry. Easier said than done.

They used to recommend that if the boat was sitting on bare ground, no cement no black top etc, that you put a sheet of plastic under it to keep moisture evaporating from the ground from slowing the drying process. I know they used to say keep the bilge dry. Our boat had tne winter canvas on it which allows moisture to move out of the boat on nice days and keeps water out.

I would not cover the boat in plastic. Did that during the repower so we could work on it and had a ton of mildew issues when we removed the plastic. Hence why I hate shrink wrap.

If you tackle the job of putting on the coating yourself, the one big piece of advice I can give you is, recruit some friends to help roll it on.

[Bertramp]

My thoughts are to haul boat end of September, put it on side of house, have it blasted, cleanse whatever the blasting doesn't get..... In spring Interprotect and bottom paint.
Boat sat in water in FL from 2009 to last week with very minimal haul time.
In the Northeast, my plan is for 06/01 - 09/30 season, shrink-wrap with breather vents and drain out .... end of story

[Amberjack]

Steve--If you dry store in the winter be sure to protect the bilges from freezing. Last winter while dry stored for the first time I had plenty of heat in the cabin and engine compartments but froze my T-12 and domestic water system located in the bilge. Always before I had wintered in the lake and lake water protected the bilges from freezing.

[Bruce]

Steve,
Might want to have someone determine if the blisters have water behind them to open and let drain and dry out during the summer before the cold weather sets in.
I've had 2 - 31's over the years that had blisters to where the boat had to sit for a few months to dry out before filling.

[Bertramp]

Bruce ... We scraped a few with a key and there was some moisture and it WAS foul smelling....
My plan is/was to have it blasted to open 'em up as soon as hauled and then do the fill and bottom paint in May, so it would be open for 7 months

[Raybo Marine NY]

Pop them, and pressure wash the bottom real good with soap and water

[Tony Meola]

Steve

What Raybo said. You need to wash them with fresh water. If you don't have too may, I would give them a good spray with Denatured alcohol to make sure there is no water taking too long to dry.