trim tabs

We just bought a 42' aft cabin CHB and in following seas I have to really slow things down(as if it doesn't go slow enough already-LOL) to keep the bow from sliding left to right and back. On my old boat (28 Wellcraft) we had trim tabs and when run down it would raise the bow and increase the control at the helm allot. Has anyone installed trim tabs on a trawler to help the control issue and also help get better speed and mileage?
Thanks
Wayne

I have trim tabs on my 7 knot trawler. About all they are good for is to help keep me from listing when my sister in law goes to the side rail.

Wayne,

I think you may have things reversed. If you drop the trim tabs the stern tends to rise up and the bow goes down. The common rule of thumb in following seas is raise the tabs to the bow comes up. The only use of tabs I can think of on a slow trawler is adding drag so I can troll. However, they would be so big to be effective I don't see that being very practical.

Tom

I've had 3 boats with trim tabs 2 outboards and one Camano Trawler. On all of them lowering the trim tabs would make the bow go down. The Camano would plane, the tabs, when lowered would get her on plane faster

Opps-you guys are right. Must have had a senior moment there for awhile. Any suggestions then on how to increase helm control in following seas. I have twin 160 turbos under the hood. I'm just not used to going this slow and before I had the power to better control the boat and get the bow up to stop the bow from sliding side to side. This as you know is the first step to a roll over.

"Fly by the seat of your pants" as in anticipating the waves' movements upon your boat. ... Found my 7-knot boat has more control at lower speeds with short-steep waves coming from the stern. ... Recommend practicing with your boat to see what works best. You might do better going faster, using the turbos. And maybe not.

Mark
Thanks for that. I tried faster but it was sliding all over the place. Slowed down and let the waves pass under the boat and it was easier to control. I just thought there might be a mechanical or apparatus solution.

obthomas said:

i have trim tabs on my 7 knot trawler. About all they are good for is to help keep me from listing when my sister in law goes to the side rail.

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D) I know exactly what you mean...my niece does the same thing but I don't complain.

Our 45' has trim tabs and when I open up the Cummins she will fly. The trim tabs help her plane faster. I have not noticed much difference at 8k. I usually cruise in the 8's. I am considering a possible rudder mod so that I don't have to steer as much. She wanders more than I like!

I dont know anything about hull design and wonder if trim tabs would make my boat plane. I have twin 210 HP Cummins and the top spped for the boat is 11.5 Knts. She is 42' with a 14'6"beam and only drafts 39". I am not sure what her displacement is but I think its around 30,000#. She does dig the stern in when running above 9 knts. Does anyone know if trim tabs would give me more speed and allow the boat to plane?

fryedaze said:

I dont know anything about hull design and wonder if trim tabs would make my boat plane. I have twin 210 HP Cummins and the top spped for the boat is 11.5 Knts. She is 42' with a 14'6"beam and only drafts 39". I am not sure what her displacement is but I think its around 30,000#. She does dig the stern in when running above 9 knts. Does anyone know if trim tabs would give me more speed and allow the boat to plane?

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Here is a picture of our hull and one of the trim tabs. Our boat has twin 270hp Cummins so I can push her a little harder. I rarely do though!

First off, Mark what the heck is that thing under you?

In a following sea, your best plan is to go just fast enough to keep your bow on the back of wave in front of you. The trouble starts when you pass over a wave or a wave overtakes you.

Seahorse, Thank you!

Good of you guys taking your "nieces" out on the boat.
An IG 36 with twin 250hp Volvos was for sale a while ago, it had trim tabs. I previously posted pics of mine, with what I know now are called small "wedges" fitted at the transom, presumably to keep the bow down.
I can`t see an application for either in following seas. If the IG with Volvos got up (?half) on the plane, it would have used lots of fuel.

Following seas are a pain, not much one can do about it. Some folks recommend "Tacking" so as to take them on an easier angle. I haven't been bothered by it bad enough, yet, to try that but it seems it would help.
Any one with experience doing that?

In a following sea, your best plan is to go just fast enough to keep your bow on the back of wave in front of you. The trouble starts when you pass over a wave or a wave overtakes you.
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True if the boat is capable of doing that. Often the waves are rolling through faster than the boat can match. My old C.C. was great in a following sea as most of the time I could run a bunch faster than the waves.

I have trim tabs on my current 7-8 K'er and although they don't help the boat go faster I can defintely see a difference in the rolling wave behind me, tab up vs down. and the bow angle change slightly, flatten. I can't measure the difference but that tells me the boat should be running a hair more efficiently.

When I'm in a following sea that is moving faster than my boat the tabs are retracted and I slow down so the waves pass under at a reasonable rate, a judgement call. When my boat speed is just a hair less than the wave speed that is when I have the most trouble with steering.

Don't be afraid to use the throttle in a burst if you find yourself in a situation where the wheel is cranked for all it's worth and the boat is still slewing. I do that, a quick burst, and it brings the boat back into line.
You don't want to increase boat speed, but when the wave is coming behind, your rudder effectiveness is reduced. The burst will get a shot of fast water moving over the rudder and straighten the boat. Just be ready as it may want to go the other way.

For the trim tabs I do believe a deeper chord plus one in the centre of the transom would help the efficiency in my case. Just a matter of if it is worth the $ and time. If the tabs take out some squat they are doing a job.

Frayedaze

Give Oliver a call at Bennett Trim tabs a call and he can tell you if tabs would help. If so what size would work for you.

HopCar said:

In a following sea, your best plan is to go just fast enough to keep your bow on the back of wave in front of you. The trouble starts when you pass over a wave or a wave overtakes you.

Seahorse, Thank you!

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Bingo - On both statements!

fryedaze said:

I dont know anything about hull design and wonder if trim tabs would make my boat plane. I have twin 210 HP Cummins and the top spped for the boat is 11.5 Knts. She is 42' with a 14'6"beam and only drafts 39". I am not sure what her displacement is but I think its around 30,000#. She does dig the stern in when running above 9 knts. Does anyone know if trim tabs would give me more speed and allow the boat to plane?

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Hi Dave

I'm not a credentialed marine engineer, by any means. However, I do have decades aboard boats, owning boats, piloting boats, and working (in my early years) with shipwrights in boat yards of NY and Maine... building, restoring, refinishing and adding items as well as sections to boats - back then the vast majority were made of wood, what fun!

It clearly appears by your picts that your boat has planing hull. Some may call it semi displacement or semi planing. The way I see it: If it can plane it's a planing hull. If it can't its displacement - Period!

Therefore, regarding your hull design, size boat, weight, power availability and whether trim tabs could make your boat plane:

It sounds by your description of digging in her stern above 9 knots (your length boat's approximate top end of its "displacement hull speed") and her top speed being 11.5 knots that you simply are just shy of enough power to pull her over the bow wave for leveling out and planing atop the water... rather than continuing to "dig in" her rear, and, push lots of water with her “somewhat upward pointing” bow. I bet she drinks fuel at the 11.5 knot speed, should be very inefficient fuel usage then as deep dig rear and bow wave push takes loads more energy per knot compared to just about any other speed (attitude in water) a boat's hull may attain.

In answer to your question... large trim tabs might (notice I say “might”) be able to help your boat barely get onto plane at WOT. But, from what you say circumstances are with current power, props and without tabs, then even with tabs I doubt you could hold plane unless staying at or real close to WOT continuously.

Couple suggestions that may help you have your boat plane. Also, I highly recommend that you discuss this with hull designers/engineers, mechanics/engineers familiar with your motors, and propeller designers/engineers.

1. Increase horse power of your engines if it is doable – somewhat of an $Ouch$ (install more powerful engines - BIG $$$-OUCH-$$$)
2. Have props designed/altered to better make use of current motor power or to suit potential for increased power
3. Have real good trim tabs that the hull engineer recommends professionally installed.

I believe your boat could probably be engineered to plane – but, it may (would) be at a cost... how tall the cost is depends on how much of a potential exists via different parameters mentioned in 1 – 3... and... how much you are willing to spend to potentially plane.

Best luck my fellow boater, and of course - - >

Happy Boating Daze!

Following seas are my condition of choice. A rounded canoe stern makes all the difference. Might be a complicated refit for the average trawler, though.

I removed trim tabs during my refit. My stabilisers keep the boat level now. The trim tabs did keep the bow down at WOT, but it was still 'ploughing' through the water rather than planing. Weight is a big factor for planing and I think a lot of trawlers are just too heavy and also have too much quarter beam buttock angle for them to plane. Trim tabs are only likely to be beneficial only if you are close to planing anyway

I think the best idea for steadying a wandering bow in following seas is something like this.
Seabrake

I have one, but haven't tried it out yet.