trim tab sizes

[lime4x4]

Okay A couple of months ago i posted about the correct trim tab size need for a 27 foot searay. Some knowledgeable people said to install 30x9 (currently have 12x12).After measuring i've come to the conclusion there going to be huge and take up almost the whole transom.Not to mention relocating the actuators further into the centerline of the boat and being placed under even more water.I've attached a picture of the boat with the current trim tabs.By the way the boat does have an issue when it comes to planing that's why i'm looking at the trim tabs.

 

[tashasdaddy]

Re: trim tab sizes

you need all the surface you can get, the get that heavy stern up.

 

[Boatist]

Re: trim tab sizes

I like the 12 inch chord much better than the 9 inch. Looking at your picture it hard to tell if the tabs are flush with the bottom or maybe 1/4 inch higher.

My 21 foot boat I have 24 wide by 12 deep and I love them can stay on plane to 9 mph but my boat only weighs 2800 pounds dry. Also my tabs are the older style, Just plane flat with no lip on either side. Mine are bigger than recommeded but I love them.

One question is what speed does your boat reach? Could you be down on power? When trying to get on plane do you still trim the motor in?

 

[Jdeagro]

Re: trim tab sizes

lime4x4;

The rule of thumb is 1" each side for every 1' in length. Most boat manufacturers do not want to do this for several reasons. Cost, trim sensitivity, and they just lie to themselves about their wonderful design. They want you to rely on your motor trim as well.

Bennet is correct, the more controlable surface area you have the more efficient you can make the hull.

Problem! Not enough room! The 12 inch deep plate is proportionately more efficient than the 9" in theory.

I would suggest that you contact Bennett customer service. They may have a different plate that will do a better job.

Keep this in mind as well:

The more weight in the boat the more water it will draft and the more difficult it will be to plane. Remove all of the excess stuff that has built up over the years.

Motor trim should be all the way down on acceleration.

Make sure the trim tab hydraulics are not bleeding or leaing. Plates stay down.

Good luck

 

[lime4x4]

Re: trim tab sizes

Motor is trimed all the way in. the boat hits about 35 mph.If i take off with the tabs up the boat maxes out at 18 mph then if i start putting the tabs it will come up on plane.If i take off with the tabs down she comes up onto plane around 25 mph i basically have to keep the engine full throttle to stay on plane even with the tabs down. i'll spend the money for the bigger tabs it just looks like overkill from my perspective.I have room for 30" tabs. Me and supernova have been playing with this boat last summer and we tried many different things to get this boat to plane sooner and stay on plane with lower rpm's with some success. I think what it comes down to is the fact that this boat is stern heavy..and not from being waterlogged either.

 

[dvan1901]

Re: trim tab sizes

I noticed there is a hydrofoil on there, you should probably take that off if you have the tabs already and see if that helps.

 

[Jdeagro]

Re: trim tab sizes

Ok, let's think about this. Since the boat will not exceed 18 with the tabs up upon accelleration, and plains out at 25 when you take off with the tabs deployed, then they are obviously working to some degree. The hydrofoil is the same as a fixed trim tab and will provide additional lift upon accelleration, however the extra plaining surface is not enough to improve the situation very much. Larger plates would be better.

What you have not mentioned is your engine rpm's at full throttle. If your are not achieving the recommended rpm range (most likely about 4800 to 5000) then you may need to change the prop pitch. Have you changed or tried other props.

I would have the prop inspected at the least, and call Bennett to see what other plate sizes they may have to work with your existing set up.

If you wish, you can call me at 800-233-0194 (Nauticus, Inc)

 

[lime4x4]

Re: trim tab sizes

Thanks the hydrofoil was removed it was put on for testing only. Current prop is a 3 blade 16X13 the engine hits about 4600 rpm's. i did talk with bennett and there saying what i already know.. bigger tabs and i'm going to have to relocate the actuators so there in the center of the tab. Just don't like the idea of moving the actuators further under the water..

 

[tashasdaddy]

Re: trim tab sizes

you have 2 choices, do it or live with it.

 

[lime4x4]

Re: trim tab sizes

you forgot the third option sell the sucker...lol

 

[Boatist]

Re: trim tab sizes

I assume this is a V8 engine. Most of the newer V8 turn 4800 rpms at WOT, of course year and model must be checked to find out for sure the manufactors recomended WOT RPMS. A tune up may get you a few more RPMS and get you on plane much faster and eaiser.

Anyway if it should be 4800 then a different style prop may help some. Going to a 2 inch lower pitch would give you about 400 more rpms and put you at 5000 WOT RPMS. 5000 is too high but a different style can make a difference. Example on my boat I changed from a 17 pitch aluminum to a 17 pitch Stainless Steel double cupped prop. The blade is thinner but also gets a better bite so I gained about 3 miles per hour. Also I belive the diameter was about 1/4 inch difference also.

Of course removing any unnessary weight will help and moving weight foward may also help.

 

[Jdeagro]

Re: trim tab sizes

Lime4x4;

Call me as I may have a suggestion.

 

[lime4x4]

Re: trim tab sizes

any particular time and who do i ask for?
thanks

 

[dcg9381]

Re: trim tab sizes

Bennet will recommened bigger tabs for that boat. They have a sizing chart on their website.

I think this is masking your overall problem, which is that your boat is underpowered/overweight for whatever reason. I wouldn't think that the boat was designed to require WOT to stay on plane w/o external tabs.