Trim tabs don’t alter pitch of boat

[AllanS]

Sorry, another newbie question. While at cruising speed, say 12-15 kts, I expected that activating the trim tabs would lower the bow, but no matter how I adjust them, they seem to have no affect. I did test the trim tabs this spring while on the hard, and then do activate when the helm switch is used. PO said “not to expect much bow down or planing out from this boat”. Something doesn’t sound right to me…thoughts?

 

[spikedaddy99]

If you are sure they are working (can you do any side to side moving?) like make port side rise while starboard dips? Mine are noticeable, but of course a different boat. There should be some threads where guys have increased the size of the tabs, or added fins to the ends to give better bow down force.

 

[Ididntdoit]

Have you verified they work?

 

[spikedaddy99]

And, are you on plane at 12-15 knots?

 

[AllanS]

My boat only does 20 kts when WOT, so I thought it would be, but I need to pay more attention to that. I prefer to cruise slower, say 10-12 kts, and the bow seems to ride high, no matter how I set the trim.
I thought the boat did not have to be on plane to have the trim be effective. I was hoping the trim would lower the bow at slower cruise speeds.

 

[Gofirstclass]

Allan, I had a similar problem when I bought Beachcomber. The tabs worked but not much. I had pieces of stainless bolted onto the tabs that enlarged them to almost double the original size. The new tabs were wider both side-to-side and also fore-to-aft.

The difference was amazing and I never had any regrets.

 

[spikedaddy99]

Allan, I had a similar problem when I bought Beachcomber. The tabs worked but not much. I had pieces of stainless bolted onto the tabs that enlarged them to almost double the original size. The new tabs were wider both side-to-side and also fore-to-aft.

The difference was amazing and I never had any regrets.

What Mike said.

 

[MiLoII]

I am not familiar with your boat and mine is very different. But ill share what i know. My boat is ass heavy and does not like to trim out at the speed you are cruising at. I suspect with those cats you can cruise much closer to you top end and if you're just plowing water at your current cruising speed you may enjoy better economy. Or you may need to slow down a bit. I added the drop fins onto my tabs and that did improve performance of the tabs significantly. I recommend you consider one of these options to either increase you tab surface as a couple here already mentioned or try the drop fins. You might also try in the interim to test with your tabs fully extended to get fully on plane at which point your boat should trim out and then back off the throttles slowly until you sense the trim changing back and the bow raising. A hundred or so rpm above that point should be your sweet spot

 

[AllanS]

Thank you all for your suggestions. Testing the integrity of the hydraulics and refitting fins or extra area to the tabs will have to wait until the boat comes out of the water in the fall. They are under the swim platform and too deep to work on with the boat in the water. In the meantime, I’ll try some of your suggestions at a variety of speeds…I am still learning how this boat reacts to different levels of propulsion. I like the idea of finding the “sweet spot”, or multiple “sweet spots”, if possible.

 

[Gofirstclass]

Allan, I knew I had some pics of the trim tab work I had done when I bought the boat but I had to go back to an old laptop to find them.

This first pic shows the trim tabs but more importantly it shows a stainless piece that I had added on to the hull to give a longer running surface. In theory that would give an ability to keep the boat on plane at a lower speed and it also moved the wake that is generated by the hull a couple of feet further aft.

This next shot shows the port tab from a side view. You can clearly see the size of the enlargement that we put on and the size of the original trim tab for comparison.

This one is pretty much the same thing but it does show how closely matched the trim tab extension is with the center piece we put on.

Got questions? Fire away.

 

[AllanS]

Thanks so much for the pics, Gofirstclass! I know how hard it is to find pics from the past, particularly before cloud storage! Yes, I have lots of questions…1. What type of boat is this? 2. Did you know in advance that trim would be an issue? 3. What thickness of stainless did you install on the transom, and on the tabs? 4. Did you gain downward pitch at lower speeds? 5. Are there two rams per tab? Mine only has one per tab.
I have pics of my transom before I launched this spring, not great at showing the tabs, but helpful for this discussion. I’ll post them soon. My SR has very large prop wells, so I’m not sure I could add transom extensions.

 

[AllanS]

Here are the pics of my 1989 440 Aft Cabin, prior to spring cleaning, so please overlook the mess! From what I see, if I did make modifications, it would be limited to the tabs, right?

 

[Gofirstclass]

Thanks so much for the pics, Gofirstclass! I know how hard it is to find pics from the past, particularly before cloud storage! Yes, I have lots of questions…
1. What type of boat is this?
It's a 1995 Sea Ray 550 Sedan Bridge

2. Did you know in advance that trim would be an issue?
No. When I bought the boat I had it shipped to a boat yard in Portland, OR. The owner has an unlimited skipper's license and also a master's degree in marine engineering. It was at his suggestion that we do those mods.

3. What thickness of stainless did you install on the transom, and on the tabs?
I don't know for sure but it was about 1/8" thick stainless.

4. Did you gain downward pitch at lower speeds?
Not really. The 550 was "pitch neutral" at low speeds. In other words the boat was pretty level at any speed up to where we started to get on plane. At that point as the boat transitioned from being "in" the water to getting up on plane where the stern would dig in and the bow lift.

As the boat came up over the hump and got up on plane the bow would drop back down, the stern would pick up and it would get up and go. Then I would use the tabs to make the boat run level. It had a tendency to run with the port side down because I had a HUGE battery bank put in on the port side to run the 5K inverter.

5. Are there two rams per tab? Mine only has one per tab.

Yes, two rams per tab.

I found out early on that the tabs provided the ability to level the boat side to side at low speeds but with those large tab additions only a little tab adjustment was needed.

Oh, and btw, spelling out gofirstclass takes too long. Either GFC or Mike works just fine.

 

[AllanS]

Thanks, Mike. Thoughts on my other questions, and potentials mods I can make to my boat, based on pics?

 

[juggernaut1]

I had the same problem. Original sized trim tabs were useless at the speeds you have mentioned. I enlarged mine an inch each side and 3.5 inches in the chord (now 26 inches by 15.5 inches) and incorporated 3 inch drop fins. Massive improvement.

 

[Steve S]

Thank you all for your suggestions. Testing the integrity of the hydraulics and refitting fins or extra area to the tabs will have to wait until the boat comes out of the water in the fall. They are under the swim platform and too deep to work on with the boat in the water. In the meantime, I’ll try some of your suggestions at a variety of speeds…I am still learning how this boat reacts to different levels of propulsion. I like the idea of finding the “sweet spot”, or multiple “sweet spots”, if possible.

If you are interested, I do have a brand new set of 12 x 30 drop fin Bennett Trim Tabs in my garage.

 

[AllanS]

The difference I see in the pics Mike and juggernaunt have provided and my boat, is that my tabs do not extend beyond the transom, but sit in a specific recess under the transom. That recess might limit my ability to install wider tabs, but certainly I could extend the chord (fore-aft) length and add vertical fins. Steve, thanks for the the offer to sell yours, but I have no idea what size mine are currently, and whether they would fit (or be made to fit) the transom recess that houses my tabs.

 

[AllanS]

Is there a significant advantage to adding extensions to the transom midships, that is, from my pics, below the drain plug?

 

[Pirate Lady]

2 cents here. I have found most factory tabs are undersized. On my last 3 SR 25 - 27’ i replaced the tabs with the 30 - 34’ size. Big difference, i intend to do it on this 25 this winter. My last 268, with the huge tabs, i could throttle back (on calm water) to 2500rpm and still stay on plane.

 

[juggernaut1]

The difference I see in the pics Mike and juggernaunt have provided and my boat, is that my tabs do not extend beyond the transom, but sit in a specific recess under the transom. That recess might limit my ability to install wider tabs, but certainly I could extend the chord (fore-aft) length and add vertical fins. Steve, thanks for the the offer to sell yours, but I have no idea what size mine are currently, and whether they would fit (or be made to fit) the transom recess that houses my tabs.

Yes your tab setup is like Riviera employs on their boats. Agreed that your only option is to extend the chord. If you go that route then definitely incorporate the 3 inch drop fin feature (mine were bent into the tab during fabrication rather than a separate bolt on) as they become more important on tabs with a longer chord to channel the water flow through the entire length of the tab.