Trim tabs

[AlaskaProf]

So, I'm a reformed sailor with a 41' semi-displacement trawler. The boat has trim tabs, which, I must confess I've never moved. They seem to be in the "stream" position, ie aligned with the bottom of the boat. I have 55 years of aeronautical experience with "trim", but I've no clue about these devices. What circumstance would call for me to move them?

 

[Ski in NC]

At slow speed, no or trivial effect.

If you are approaching planing speed, with tabs down the transition speed is lowered.

So tabs down, boat might be planing (sort of with SD) at 14kts.

With tabs up, planing might be a few knots higher, like 17kts.

If in those transition speeds, down tab can mean bow down, which is usually a good thing.

Play with them to see the effects.

 

[C lectric]

I have them on my non planing boat and they have uses.
Trim side to side can be affected by using.
Fore/aft trim can be affected.
Reduces large rolling stern wave when pushing the boat speed.
Your specific boat May not benefit but try them, play with them.


In following seas I back them fully off or they can help the bow to dig in--not good.

 

[Art]

As others have said: Play with them at different speeds and in different wave conditions and when out of sync port to starboard weights may be aboard boat.

TT's are interesting "levelers" or general attitude "adjusters" to have fun with and to make cruising just a bit easier.

 

[eyschulman]

Have them on my SD and as Sky says but would add they can also help trim side to side by adjusting one side. My boat at 14-16K gets 1 to 1.5 extra K when I push the nose down. There is no visibility issues on my boat at speed but some boats go nose up and are helped in this department by tabs. I did not think I would need them the builder wanted them. Not needed but helpful and I use them regularly. Play with yours see what they do.

 

[AlaskaProf]

Thanks all for the prompt responses.

I have fuel "crossfeeds" for trim on the "roll axis" and so far prefer hull-speed cruising (remember, I'm stepping up from 20-somethin-foot sailboats 8 knots still feels pretty good. ), but I gotta say the eye-watering, pheromone-generating, hat-blowing effect of getting on-the-step is not entirely lost on me, so next time out we'll "open 'er up" and report back on the tabs.

 

[Art]

Thanks all for the prompt responses.

I have fuel "crossfeeds" for trim on the "roll axis" and so far prefer hull-speed cruising (remember, I'm stepping up from 20-somethin-foot sailboats 8 knots still feels pretty good. ), but I gotta say the eye-watering, pheromone-generating, hat-blowing effect of getting on-the-step is not entirely lost on me, so next time out we'll "open 'er up" and report back on the tabs.

Too Cool! Have Fun!

BTW - I recommend that before you go out to do "TT Play" [sounds sexy - doesn't it!] you do a visual on the tabs.

Older boats sometimes have trim tabs that may be stuck in position if not used for long time. I.e. - Have someone push the toggle (or toggles if one is at each pilot station) all the way forward to make sure the tabs are responding correctly/fully and all the way back to see the tabs also respond correctly/fully in opposite direction. Additionally, check the tabs hydraulic fluid's container to make sure it is full.

The toggles usually have response info printed there.

Pretty simple - trim tabs down lowers bow, tabs up raises bow, tabs flat plane with bottom eliminates effects. Alternately adjusted tab positions makes boat heal port or starboard in corresponding attitudes to up or down per tab adjustments. Toggle switch will let you play with the tabs' positions similar to flaps on a wing.

 

[gaston]

32 IG 315hp Cummins 2400 rpm pushing hard into a nasty sea last Thursday and the trim tabs lifted the bow far enough to stop the wave going over the bow. Yes I think they are a nice addition

 

[Keysdisease]

And to add to what Art says, you mentioned aircraft and so I thought you might want to know the control for your tab may look like it's wired "backwards." That's because its designed to be intuitive. For example Stbd bow down will activate the Port trim tab to go down which will put the Stbd bow down.

Bennett, which you probably have, has an excellent site. Because these may not have been used for a long time note that 95% of issues are electrical and can be fixed easily and inexpensively

www.bennetttrimtabs.com

Too Cool! Have Fun!

BTW - I recommend that before you go out to do "TT Play" [sounds sexy - doesn't it!] you do a visual on the tabs.

Older boats sometimes have trim tabs that may be stuck in position if not used for long time. I.e. - Have someone push the toggle (or toggles if one is at each pilot station) all the way forward to make sure the tabs are responding correctly/fully and all the way back to see the tabs also respond correctly/fully in opposite direction. Additionally, check the tabs hydraulic fluid's container to make sure it is full.

The toggles usually have response info printed there.

Pretty simple - trim tabs down lowers bow, tabs up raises bow, tabs flat plane with bottom eliminates effects. Alternately adjusted tab positions makes boat heal port or starboard in corresponding attitudes to up or down per tab adjustments. Toggle switch will let you play with the tabs' positions similar to flaps on a wing.

 

[Art]

And to add to what Art says, you mentioned aircraft and so I thought you might want to know the control for your tab may look like it's wired "backwards." That's because its designed to be intuitive. For example Stbd bow down will activate the Port trim tab to go down which will put the Stbd bow down.

Bennett, which you probably have, has an excellent site. Because these may not have been used for a long time note that 95% of issues are electrical and can be fixed easily and inexpensively

www.bennetttrimtabs.com

What Keys says is very true!

Just want to mention: When we purchased our 1977 Tolly 9 yrs. ago from orig owner she was in great condition. However, seems the owner had not used the trim tabs for a l-o-n-g time as their hydraulic reservoir had but drops left in bottom. I thought oh crap... there's a leak and probably air bubbles in the lines too. So... I filled it up before at all checking either tabs hudraulic ram movements to try and be sure to not let an air bubble get pushed-into/trapped in the lines. Well, it worked out better than I had figured. There seemed no air bubble and both tabs worked perfectly. Also from day I filled it 9 yrs. ago the fluid level has never dropped. Go figure?? Where had the fluid gone to produce empty reservoir when we purchased???

Additionally, I recommend exercising the tabs with full throw at least a few times a year even if not needing to for cruising. IMO, that exercise keeps the ram shafts and O rings in best condition. Our Tolly has Bennett Tabs

Happy TT Daze! - Art

 

[RT Firefly]

Greetings,
Mr. g. Re: post#8. "...the trim tabs lifted the bow far enough..." Any time I've engaged the TT's, they push the bow down. If the TT's are fully retracted (in an up position) AND the bow is down, lowering the TT's simply pushes the bow down more. Explain your experience please.

 

[Dixie Life]

Maybe after all these years I really don't know what trim tabs are used for. Can someone tell me why anyone would put trim tabs on a full displacement trawler?
Just asking.

 

[Lou_tribal]

Maybe after all these years I really don't know what trim tabs are used for. Can someone tell me why anyone would put trim tabs on a full displacement trawler?
Just asking.

Same reason as why a teenager put a big wing on the trunk of his Honda Civic... to look like a racer

L.

 

[Dixie Life]

Now I know.