Trim Tabs on my 31

[Ironworker]

Hi,
My first post on the Bertram 31 forum. My friend and I are refurbishing a 31. I'm about 3 months from getting this boat in the water. My question is whether I should add trim tabs to the boat. This boat currently has Volvo Diesels 220 HP but repowering may be in the near future.

I'd post some pictures but do not know how to do so on this site.

[Tony Meola]

Welcome

Trim Tabs on a 31. Well this is a subject that gets visited often on here. Actually, if the boat is balanced correctly, you really do not need them. I would run her without them for a while and see what you think. I don't think we have ever taken an actual count of who has them and who does not, but I would say the majority do not.

For posting pictures most of us use imgr. If you go to the top of the General Discussion page you will find a lengthy discussion on posting pics. You should just skip down to the posts in the last 12 months. Everything changed when Photo bucket stopped playing nice.

Again welcome and do not be afraid to ask away.

[Carl]

Welcome aboard.

Tony is right...use it for awhile and decide for yourself.


I ran boat a little over 10 years without and rarely if ever felt a need for them.

That was till I had to change the 170gal fiberglass fuel tank to a 220 gal alum tank...Thank you ethanol for eating my tank.

Boat still ran okay when tank was full to mostly full...but a 1/2 tank or less of fuel, with tank being longer all the weight of the fuel went aft as I brought up the throttle.
Once on plane, boat leveled off and it was fine...but I had to keep a faster cruise and that is not always what I wanted.
Sometimes I wanted to just run slow below 17-18mph or so and at those speeds the stern sat and dragged or boat just fell off plane...adding tabs solved that issue.
With tabs I could lift the stern a bit at slow speeds and stay on plane, great economy, easier ride for the family, the inlaws.

You have alot more weight with diesels midship, so slow speed may not be an issue for you compared to my ol-440 gas motors.

So back to the original, Tony is right...use it for awhile and decide for yourself.

[Ironworker]

Thanks for the suggestions. This boat also has a new 220 gallon fuel tank and we've added a tower on the boat. This has been an overwhelming 12 year project but we've closing in on the finish line. I need to take the time to document this project on this board.

I've visited the site several times looking for articles/suggestions but was not aware there was a discussion forum. I'm looking forward to being part of the community.

[mike ohlstein]

What model is it?

[Ironworker]

Its a 68 Flybridge model. As soon as I can figure out how to post photos, I'll get some uploaded.

[mike ohlstein]

Open a free account at IMGR. Upload your pictures. Right click on the image and copy image location.

Post here by hitting the IMG button and pasting the image location in between the two IMG icons.

Or, open a free Dropbox account. Upload your images, and then just post a link to the directory.

That would look something like this:

https://www.dropbox.com/sh/nzbv9gt6bsxs ... uYwRa?dl=0

[Ironworker]

Lets give it a try....

[Ironworker]

I'll try again.


https://www.dropbox.com/sh/j2ij8muk1pen ... LP3_a?dl=0

[mike ohlstein]

I fixed your top image. If you had right clicked and 'copy image location' and then pasted it, it would have worked.

If you 'edit' that post, you'll see what I did.

If the image is very large, this website will trim it in a way that you won't like. Better to upload images under a meg.

Nice work, by the way.

[Ironworker]

I fixed your top image. If you had right clicked and 'copy image location' and then pasted it, it would have worked.

If you 'edit' that post, you'll see what I did.

If the image is very large, this website will trim it in a way that you won't like. Better to upload images under a meg.

Nice work, by the way.

Mike,

I appreciate the assistance. Once I get the photo deal down, I'll post a few more pics.

Rick Ott

[JH_B28]

First one i've seen with a transom door. Nice work.

[Carl]

Rick-

Wow, shes looking great!
I'd say a considerable amount of work went into that...

I'd gander the diesels and tower offset the weight of having additional fuel in the stern.
Tabs can always be added down the road.
Plus they can't get in the way, break, leak, be left down when backing down AKA-ripped off or running in snot with them down(great way to bury the nose) if you don't have them.
Aside from low speed cruising the boat really doesn't need them.

[Ironworker]

I appreciate the kind comments. My buddy Jim started the project then passed it along to me to finish. Even with all the work that has been done its still a pretty overwhelming project to finish.

This boat is going to be a fishing machine when completed. The boat is headed to the Bahamas and will live there year round. We installed the transom door to drag the wahoo/tuna through and an occasional SCUBA diver.

One of the features, that I'm going to post some pics of is the 3 KW chirp transducer which is installed in a pocket in the keel.

[David Davidson]

I fitted Volvo Interceptor trim system to my 31. They have no tabs to get snagged.
https://www.volvopenta.com/marinecommer ... m-450.html
They work well but I very rarely need them. I have Yanmar 240s and a 170 gal tank

[Tony Meola]

Nice work.

Not sure why Carl's boat came off a plane so easily with the 220 gallon tank. My 31 came through with the 220 gal tank and with the Big Blocks, full tank and loaded but no tower, she would plane at around 1400 RPM's and would easily stay there. When really loaded, 50 gallons of extra fuel, about 300 lbs of ice and 4 or 5 guys, heading offshore. The fuel and Ice at the transom, yes she dragged a little but still planned and held a plane at easily at 15 knots.

With the diesels it will be easier to plane her off since you are turning a bigger prop and have more torque.

Not sure how the tower will impact you.

[Carl]

Not sure why Carl's boat came off a plane so easily with the 220 gallon tank.

Tony- problem is you have nothing to compare to. Having had the smaller tank that was fitted closer to midship I was able to experience how easily the boat popped up on plane as I brought up the throttles....especially when lighter on fuel.

Soon as the larger tank went in I noticed that I needed to push up the throttles a bit more to get over the hump. Then as the tank went to less then half ...getting started took even more throttle as the fuel all went to back of tank which made the stern heavy and we had some time spent squatting, which was something boat only did when really loaded with sizable people sitting at stern. That was till boat came up on plane, starting to level off. Basically it was like a couple big guys sitting on the transom when powering up.
Yes, all solvable with more throttle and something you get used to, just push them up further, faster.

Aside from the way the boat felt, I could see what was happening using the Flo-Scans. Prior to the larger tank I'd cruise at 10-11gph per engine, larger tank it was 11-12 when light and closer to 13-14 when heavy. Tabs brought me down to 9-10gph per engine.

When running someplace to get there...no big deal, push the throttles up and go.
But then sometimes for a howdy cruise it was just a ride for half hour, hour with no place in mind to get to... at those times I had time to play with throttles to find a sweet spot that burnt less for the same speed. Or played with tabs and throttles and flowscans...could easily pickup 2knots by putting tabs down at slow cruise with same burn. Or put tabs down and cut down on throttle and drop a gallon or two an hour.
When fuel was low with larger tank...playing at those low speeds it did not take much for boat to fall off plane...then it was time to push the throttles up again. And when I say fall off plane...boat might technically still have been on plane...but its the point when speed dropped significantly for same rpm, same burn...