Need Help With Too Small Trim Tabs

[dpmulvey]

[FONT=Verdana, Arial, Helvetica][FONT=Verdana, Arial, Helvetica][FONT=Verdana, Arial, Helvetica] My 1999 330 Dancer is pathetically under tabbed. I believe they are 22X9. I cannot fit 33X9 tabs on the current setup. Has anybody modified their tabs to provide more stern lift?[/FONT][/FONT][/FONT]

 

[fc3]

You can contact Bennett and get different trim cylinders. I installed 3/4" spacers between the tab and cylinder which give another 3/4" of tab extension. I didn't want to change cylinders.

Looks like this. It's an old codec that you may not have. I doubt I have the original animation to re-encode it. And I doubt I remember how to use 3ds MAX, which only runs on windoze.

Best regards,
Frank

 

[LMBoat]

DP, I have a '95 330 that had the exact problem when we bought it 6 years ago. I went through a variety of options and came up with this: Your current trim tab cylinder probably has 2 1/4" of travel <mine did>. You need one with 3" travel <at least this is what worked for me>. This made a phenominal difference in handling and bow rise when coming up on plane. The Bennett part# is 12062 <954-427-1400>. They will tell you this is for a Viking, but this is what solved my problem. Bennett swapped mine out for free. Even if you have to pay for them it is the solution to your problem. If you just add a spacer block, your tabs will always be somewhat deployed <more drag>.

 

[fc3]

If you just add a spacer block, your tabs will always be somewhat deployed <more drag>.

On my 330DA, the tabs retracted well beyond the bottom of the boat. With the spacer, the tabs are slightly above the running surface. Thus when fully retracted, the have no effect.

Sea Ray seems to have mounted the trim cylinders too high. They might have mounted them that high to limit the maximum amount of bow down trim. Just Ducky runs pretty flat at higher speeds. I could see some boob pushing the throttles up and leaving the tabs down which will cause some wicked bow steering.

Best regards,
Frank

 

[keokie]

You may also be able to get a tab that is 12 deep inches rather than 9. I'm not sure if they make a 12 inch that is 22 wide, but it would be worth a check.

 

[fc3]

You may also be able to get a tab that is 12 deep inches rather than 9. I'm not sure if they make a 12 inch that is 22 wide, but it would be worth a check.

Deeper planes would exacerbate the reach problem of the trim cylinders.

Best regards,
Frank

 

[dpmulvey]

Great help. Please keep the suggestions coming. FC3, I shall have to check the final full up position of the tabs. I have attached a few pictures of Mrs. Robinson's tabs that I took a couple of days ago. IIRC, my tabs are the same.

They run 22 inches at the transom and taper to 19 inches at the end of the chord. I have 5.5 inches on either side to play with should I decide to expand the width and XX inches to play with in chord.

This is going to get interesting!

BTW, I found something interesting. There is a hook in the prop pocket to provide lift. Don't know how effective it is considering the angle of the props, but it is there none the less..

 

[keokie]

On the 12 inch deep tabs, the extra 3 inches is added past the trim cylinder so they deflect at the same angle, but extend a bit further.

 

[fc3]

I'll grab a photo of my tabs next time I'm down by the boat. I can't drop the tabs since the boat's shrinkwrapped and I don't want to cut to get inside. I'll try putting a straight edge on the bottom so you will be able to see the amount of clearance pretty easily.

Remember your grammar school arithemetic. A^2 + B^2 = C^2
So if A is the distance from the pivot of the trim cylinder to the tab's hinge and B is the depth of the tab from the hinge to the cylinder's mounting point, and C is the length of the cylinder from the pivot to the mounting point on the tab, you can see that as the tab depth gets bigger, the length of the cylinder has to get longer, and that just keeps the tab in it's retracted position!
(The Pythagorean theorem is for right triangles, which describes the geometry of a retracted tab.)

If arithemetic doesn't do it for you, get a cardboard and tape it to the side of your desk. Put a pencil where the trim cylinder goes. Now see how much longer of a pencil you need when you use a bigger piece of cardboard.

If your trim cylinder doesn't deflect the tab down enough now, it really won't when you go from 9" to 12".

Best regards,
Frank

 

[keokie]

Fc3, You are miss-understanding my point (or I am not making it effectively). Maybe this will make more sense. If you lengthen your current trim tab by 3 inches aft, but do NOT change the location of where the cylinder attaches to the tab, you will maintain the same deflection. The benefit is the extra 3 inches gives you more surface area and slightly better leverage.

Years ago on another boat, at Bennet's suggestion, I changed from a tab that was 12 inches wide by 9 inches deep to one that was 12 by 12. The trim cylinder mounted 3 inches ahead of the end of the new tab (the old one mounted right at the end). It produced the same deflection, but with a larger tab. The difference in performance was very significant.

 

[fc3]

Fc3, You are miss-understanding my point (or I am not making it effectively). Maybe this will make more sense. If you lengthen your current trim tab by 3 inches aft, but do NOT change the location of where the cylinder attaches to the tab, you will maintain the same deflection. The benefit is the extra 3 inches gives you more surface area and slightly better leverage.

Years ago on another boat, at Bennet's suggestion, I changed from a tab that was 12 inches wide by 9 inches deep to one that was 12 by 12. The trim cylinder mounted 3 inches ahead of the end of the new tab (the old one mounted right at the end). It produced the same deflection, but with a larger tab. The difference in performance was very significant.

Nope, I'm not missing the point. A 12X12 tab (12 being the width along the transom) will not extend to the same angle as a 12x9 tab. Mathematically, it isn't possible. Without all of the variables, I can't calculate it, but the difference might be small or large depending on the other geometry.

Before swapping the tabs, he should measure and calculate that he'll actually gain something.

Best regards,
Frank C.

 

[keokie]

Frank the 12X12 and the 12X9 can deflect at exactly the same angle. I've made the change.

Think of it this way. If you welded a 3 inch plane of metal to the aft end of your trim tab, it would make it longer than it currently is, give it more surface area, and theoretically more leverage. It would deflect just as far because you would have changed nothing about the mounting of the trim cylinder. That is how all the 12 inch deep tabs I have seen are made.

On the 9 inch tabs the trim cylinder mounts at the end. However, on the the twelve inch tab the cylinder mounts nine inches from the hinge. This puts the cylinder mount the same distance from the transom on both, but leaves 3 more inches of tab behind it.

 

[fc3]

On the 9 inch tabs the trim cylinder mounts at the end. However, on the the twelve inch tab the cylinder mounts nine inches from the hinge. This puts the cylinder mount the same distance from the transom on both, but leaves 3 more inches of tab behind it.

That makes a big difference. Thank you for clearing that up.

Best regards,
Frank

 

[ippa2]

Sorry for resurrecting an old thread...
Frank what did you use for the 3/4" block to extend your trim tabs? I thinking of using starboard, but would be curious to know what other people have used.

Also in hindsight do you think 1" would be over kill? I am planning on retracting my tabs all the way and seeing how much it will take to get them flush with the bottom of the hull and then add that much as a spacer.

Thanks!

 

[dpmulvey]

Here is what I did. It works for me. My tabs are now 22(w) x 18(d)

 

[ippa2]

I like the idea of enlarging the tab itself, however the addition of a spacer block to where the tab attaches to the actuator is so much easier for someone who is not good with fabricating metals...

 

[Tabman]

I like the idea of enlarging the tab itself, however the addition of a spacer block to where the tab attaches to the actuator is so much easier for someone who is not good with fabricating metals...

Depending on the shape and size of the original Trim Tab a larger one can often be purchased and installed quite easily. This is preferable to adding spacers and much easier than welding.

Tom McGow
Bennett Marine

 

[ippa2]

Thanks Tom. However the biggest problem I seem to be having is that when the tabs are fully deployed they are just barely below the hull. On past boats with the tabs all the way down they extend a good 1"-2" below the line of the hull. So I was thinking the spacer would help get the tabs down below the hull so they have an impact on my running angle. I realize I could also put new actuators with more travel, but again the spacer seems like the easiest fix for now.

 

[Tabman]

Ok, that makes sense, the "standard" stroke on an actuator is 2-1/2". On a 9" chord (fore to aft measurement) the trailing edge of the Trim Tab is normally 1/2" above the hull bottom when retracted and on a 12" chord Trim Tab it is 5/8".

This translates into about 15-20 degrees of maximum Trim Tab deflection, which is optimum. Deflecting the Trim Tab more than that tends to create more drag than extra lift.

By the way I see you have Buzzards Bay as your location. I went to school in Marion (a long time ago) and sailed all over Buzzards Bay. One of my best friends lives in Falmouth and I get up that way once and a while. Where do you sail out of?

Tom McGow
Bennett Marine

 

[dpmulvey]

I like the idea of enlarging the tab itself, however the addition of a spacer block to where the tab attaches to the actuator is so much easier for someone who is not good with fabricating metals...

Trust me. That is NOT my fabrication, just my design with the help of Bennett. A local welding shop did it for me. She handles like a completely different boat.