posted 09-22-2005 06:36 AM ET (US)            

The Bennett tabs I removed were close to even with the bottom. I think this contradicts the Bennett instructions.

posted 09-22-2005 08:43 AM ET (US)            

Jim, unless the recollection you cited is in reference to the sponson profile that is below the tab hinges that I just talked about, those tabs must have been useless. There isn't enough travel in trim tab actuators to accomodate a setting "several inches" above the deadrise line, and still have travel left to exert effect on the water coming under the hull.

I notice the Lenco tabs that BW installs at the factory are installed right on the deadrise line.

posted 09-22-2005 10:09 AM ET (US)            

That is the condition that I tried to describe above on my Outrage 22. With a 12" wide tab mounted as far outboard as possible on or near and parallel with the deadrise line, (which I believe is the preferred location), but short of the reverse chine, the tab crosses the sponson as you and I have described. Recognizing the loss of efficiency caused by that condition is why I would now mount them right on the extended deadrise line. Mine work OK like they are, and I continue to be very pleased with them, but I think they would work even better by reducing the loss of efficiency caused by the sponsons.

Tabs could theoretically be mounted far enough inboard on an Outrage 22 so as to be entirely over the uninterrupted deadrise portion of the hull bottom, and would be more efficient per se, but the tabs would then be in the way for the potential of mounting an auxiliary motor, and possibly in the way of transducers, etc., as well as no longer acting from as near as possible to the outside edges of the hull bottom.

It is an interesting thing about the way my upper actuator brackets fell half way on and half way off the thickened transom area with the tabs located as I have described, because Jechura mounted the same tabs in the same place, or nearly so as far as I can tell, and his upper actuator brackets fall completely on the thinner transom section. I don't think there is any difference in hull or transom configurations from one year to another, but I'm thinking Jerry might have mounted his tabs just a little lower, and maybe just a little further outboard, perhaps crowding the reverse chine a little more than I did. And there is probably a little play in the joint of the lower actuator bracket that might allow a little fudging to avoid straddling the break line in the transom, when added to the other factors.

posted 09-22-2005 11:45 AM ET (US)            

If a doel fin is touching the water when your boat is on plane, then your motor is mounted too low. These fins should be clear of the water when the boat is on plane if the engine is installed properly.

I am convnced that the reason 95% of people who install these things is that they are trying to correct problems that would be better solved by moving the engine up a hole or three.

Also, tabs give you the ability to correct a list induced by a crosswind or uneven loading of people/cargo in a boat.

posted 09-22-2005 01:12 PM ET (US)            

I think I am going to put a 3/16 or so shim between the actuator and the trim tab so the tabs run a bit deeper when full down. Adding a "pad" to the bottom of the trim tab has crossed my mine too.

The 12 x 12 would have been better for my boat, but with transducers and a kicker motor the 12 X 9 was a better fit.

Advantage of the Lenco trim tabs is you do not have to run the wiring through the transom at the point of attachment of the actuator to the transom, you can run the wire over the transom, or through the transom anywhere you choose. The Bennett hydraulic line attachment is where the actuator is attached on the transom, no options.

Rich

posted 09-22-2005 05:46 PM ET (US)            

Some other advantages electrics have over hydraulics (tabs) is less stuff to contend with on the install, less stuff to find room for (hydraulic pump and reservoir), and quicker and crisper response.

posted 09-22-2005 08:39 PM ET (US)            

This is the installation on Jerry's OUTRAGE <jechura>. It looks to me like a nice compromise between having the tabs mounted further inboard--which leads to difficulties mounting the actuators--and mounting the tabs a bit farther outboard.

posted 09-22-2005 09:29 PM ET (US)            

The only difference between John installation and mine was that he clipped the inside corner of the stainless at a 45 degree in order to try and maintain Lenco's preferred measurement from the chine. If you look at John's site in his technical, you will see that he had to drill a new mounting hole. That 1/2 inch clip brought the actuator over on the notch. I just rounded the corner.

Both ways work with the same results. With Johns way gaining maybe a percentage or two of effectiveness.

I do agree with John that the total effectiveness of the tab is maybe 50 to 60% which normally is fine, however on the Isle Royale trip My boat was extremely stern heavy with added gas, coolers equipment etc. The tabs were all way down for the and the engine trimmed all the way in to keep the bow down. In fact when we { Gambler } pulled the boats at Copper Harbor and kissing the old 235 for it's performance, I pointed out to David that the tabs were still all the way down.

I think the pad idea will raise the effectiveness 20 to 30 % and it on my to do list this winter.

posted 09-23-2005 12:46 PM ET (US)            

If you mount the tabs as low to the deadrise as possible, preferrably right on it, I think you will gain a little room where you will not have to move the tabs quite so far to the outside to have the actuator tabs fall flat on the transom. This is due to the angle of the thicker part of the transom as it travels to the deadrise. You'll still need to trim that inside corner of the mounting bracket to achieve this tightness though.

This should achieve some better effiency than John and Jerry's initial install. How much is very hard to know.

posted 09-24-2005 11:15 AM ET (US)            

From looking at the above photos of your trim tabs it appears they are mounted too high off the bottom of the boat to be really effective. I would think that when fully lowered (down) only the back half of the tab is actually contacting the water. In essence isn't this like having 12"x6" tabs on the boat? This may be why you had to keep them fully down on the Isle Royale trip.

Steve

posted 09-24-2005 06:28 PM ET (US)            

Put a zinc on it to protect from corrosion just like any underwater metal. When you paint the bottom just paint the trim tabs.

As I understand the primer you use on the trim tab is very important before applying the antifouling so the metals in the antifouling do not cause corrosion of the tab. The primer acts as a barrier coat to the antifouling paint.

I primed my trim tabs with zinc chromate primer before applying the antifouling paint. When I haul out for the winter I'll see how that worked out. You should use the system that the antifouling paint manufacturer suggests for the paint and type of metal.

Long story short, if you properly prep the trim tabs for paint, use a good antifouling paint and put a zinc on each tab you will not have any problems with the trim tabs in salt water. The benefit of having the trim tabs will far outway any minor maintenance you will have to do to protect the trim tabs in a salt water environment. The trim tabs are stainless steel so they are very resilient to adverse environmental conditions. The zincs and painting just become part of the spring pre-lauch ritual and require no more care than the bottom of the boat during the season.

The 22 hull looks like it is tough to pick a location to mount the trim tabs. I do agree with Steve that they appear to be too far up to be effective. I am not familiar with the boat so I really do not have a suggestion, I would like to see how others have mounted them.

Rich

posted 09-24-2005 09:17 PM ET (US)            

They are mounted correctly. The way Jimh took the picture gives you that optical illusion.

On the Isle Royal trip I knew I should have loaded it more evenly.

posted 09-24-2005 10:19 PM ET (US)            

This mounting position has advantages:

--puts the whole tab right at the bottom of the transom.
--the actuator mounting is straightforward; the actuator support falls onto the thicker center portion of the transom.

The drawbacks seem to be:

--tabs are farther inboard so less leverage
--works only if using a single engine and no kicker

I like the way Rob integrated the bonding ground electrode with the tab.

posted 09-24-2005 11:32 PM ET (US)            

I think John put the tabs in place before the auxiliary engine. The mounting position for the tabs worked out well--good planning, John!

posted 09-25-2005 08:52 AM ET (US)            

I just took 4 more detailed shots of my installation and sent them off to you.

posted 09-25-2005 10:22 AM ET (US)            

The Port tab installation. Notice how the hinge has been cut back to fit against the transom center section. The actuator is an Edge Mount style, which reduces the height needed to about 11-inches from 15-inches with the Standard Mount style. This position allows room on the transom for an auxiliary motor. As Jerry mentioned above, when the hinge is trimmed to fit like this, a new mounting hole has to be drilled at the inboard end:

----

The Starboard tab trimmed up. This shows the relationship between the tab, the central V-hull and the sponson. If you look closely you can see a pencil line which extends the line of the central V-hull onto the area above the sponson.

posted 09-25-2005 10:40 AM ET (US)            

Three cups, but it was a blend of Leelanau Sumatra and Kenya...(working on #4 now, and my typing is breaking a new speed record for me - probably about 9 wpm after I deduct the time needed for corrections).

It's funny how the camera's eye shows *everything* - what is also clear on the photo showing from the underside of the tab is that I missed part of the hull the last time I cleaned it!

John

posted 09-25-2005 11:02 AM ET (US)            

Shoot, you are typing too fast this morning. As I'm typing you just answered my question.

What would happen if we mounted the tab not exactly parallel to the deadrise?

posted 09-25-2005 02:12 PM ET (US)            

Right you are- - pivoting the tab hinge as I described above would cause the upper actuator bracket to fall entirely on the thinner section of the transom.

Jerry-

I still think the best way to gain the most efficiency would be the pads - I am concerned though that if we followed the actual shape of the sponson section, the sharp nearly vertical surface (though short) of the pad could put some really considerable lateral strain on the hinge to transom connection on the inside tab in a tight turn with the tabs deployed. I wish you'd try it out... ;-)

posted 09-27-2005 12:18 PM ET (US)            

http://www.qlmarine.com/pdf/QLBTS4pEng.pdf

It would seem to me that it would be much easier to mount these tabs in such a way as to avoid the sponsons, and perhaps they wouldn't interfere with a kicker at all, as they only look to be an inch thick. Only issue I can think about is how you would run the cables to tabs on a whaler.

That is, assuming they work. Who wants to be the gunia pig?

posted 09-28-2005 09:44 AM ET (US)            

Mount the tab hinge on the central or thicker portion of the transom, but extend or overlap it outboard so that if follows the deadrise line of the v-bottom out to the sponson! You would have to make a shim or filler (perhaps from teak) to bridge the 0.75-inch (or so) gap between the hinge and the transom on the outboard portion. This would be a length of about 4- to 5-inches (judging from the pictures of a 12X12 tab on John's installation). You could drill holes for the mounting screws to pass through the filler and fasten to the hull. You could also use adhesive to attach the filler to the transom.

The advantages of this approach:

--actuator mounting will be on wood-reinforced transom area;
--no interference with tab efficiency by sponson
--tabs are outboard as far as possible and still in-line with deadrise

The disadvantage:

--you have to fabricate the fillers or shims
--the tab location would interfere with tie-down straps to the towing eyes

posted 09-28-2005 01:47 PM ET (US)            

I have twins, and you can definately adjust trim on the engines individually to correct leans.

Twins will also plane at a lower speed than a single, but you don't get the same kind of bow-down from having the engines tucked all the way in that you get from having tabs down.

It really depends on what your primary objective in having tabs. Twins give you part of it, but not all.

posted 09-28-2005 04:17 PM ET (US)            

The main benefit of trim tabs is to adjust the attitude of the boat - bow down, listing, etc., and trim your engine so that it's thrust is parallel to the hull bottom which is the most efficient for the engine.

I normally do not adjust my engine trim at all once I have it trimmed properly (which is parallel to the hull bottom). I then use the trim tabs to adjust the boat's attitude depending on sea conditions.

When you trim the engine in to lower the bow, the engine thrust is down (at an angle and not parallel to the hull) and much of the power is being used to push up on the transom rather than being used to push the boat forward. This results in inefficient use of the engine.

As David mentions, with twins, one engine can be trimmed in to correct for a list, but again that would not be the most efficient way to run the boat.

Steve

posted 09-29-2005 04:12 PM ET (US)            

I've got to disagree with you on whether it matters if you push the bow down by changing the thrust vector (trimming the engines) or changing the effective hull shape (trim tabs). In either case you are essentially doing the same thing - namely lifting the stern using the power of the engine.

I guess what I'm trying to say is using trim tabs isn't "free" from an energy usage perspective. On a boat with trim tabs, the force used to lift the stern when the tabs are deploted is subtracted from the total propulsive force provided by the engine, just the same as it is

I do agree that trim tabs give more versatility that one gets simply with engine trim, but I don't believe it changes efficiency with a given motor and a given running attitude.

posted 09-29-2005 05:46 PM ET (US)            

But I'm going to agree with Steve even more, in that, while I don't have the tools to prove it empirically, I am fully convinced (beyond all shadow of a doubt) that it is "more expensive" to raise or laterally trim the stern with the thrust of the motors than it is to do so with trim tabs, keeping the thrust of the motor(s) in line with the movement of the boat.

posted 09-29-2005 06:20 PM ET (US)            

I respectfully disagree with your statement that "On a boat with trim tabs, the force used to lift the stern when the tabs are deploted is subtracted from the total propulsive force provided by the engine, just the same as it is."

Read the he following 2 paragraphs which were taken directly from Bennett's web site:

TRIM TABS AND POWER TRIM
It is a common misconception that if a boat has power trim on the outboard or outdrive it does not need trim tabs. Power trim can be used to adjust the boat's attitude, but it is highly inefficient. A propeller is designed to force the boat forward. When trimming the boat with the prop, the prop must not only push the boat forward but raise the stern as well. In this situation, prop slippage is greatly increased thereby wasting RPM's. Power trim cannot correct listing, and is ineffective at slower speeds. Bennett Trim Tabs, in combination with power trim, enable both the hull and prop to be trimmed independently. The trim tabs trim the hull, while the power trim adjusts the prop. The result is optimum performance and efficiency not attainable by the use of power trim alone.

To achieve maximum performance, first adjust the trim tabs to achieve the desired running attitude. Next, use the power trim to position the propeller thrust parallel to the water flow. If necessary, re-adjust the trim tabs to fine tune the attitude. By observing the boat’s speed and engine RPM's the best combination of trim tabs and power trim will be apparent. Trim tab angle indicators and a power trim angle indicator are particularly useful in duplicating effective settings.

posted 09-30-2005 08:14 AM ET (US)            

Trim tabs do an excellent job of correcting a listing problem. My 21' Walkaround can seriously list with a cross wind, especially with the canvas up. The trim tabs correct this very nicely. IMO, the best thing since sliced bread!

posted 10-03-2005 10:54 AM ET (US)            

Power trim CAN correct listing on a boat with twins.

Trimming the motor(s) can IMPROVE the performance of the boat.

Trim tabs DO come at a cost to performance. They add a lot of drag which SLOWS the boat down.

The notion that the motors should always be trimmed align the prop thrust parallel to the water flow is flawed. There are often times when you do not want this to be the case.

The problem with the Bennett argument is that it assumes all you are ever trying to do is bring the bow down. That is all trim tabs can do. They can do nothing to lift the bow. Your outboard(s) can.

I have Bennett trim tabs on my 1988 Revenge 25 Walk Through. They are mounted much as John Flook's are, outboard of the center transom area and well above the sponson on their outboard half but more or less flush with the V hull.

I also have twin 150 outboards. The motors can be trimmed to correct list TO A POINT, but in any sort of a strong cross wind I MUST use (a) trim tab to correct the list.

The Revenge models do not need any help bringing the bow down. Usually I trim the motor out a bit to help lift the bow and increase speed and efficiency. Any time I lower a trim tab to correct for list I increase the drag of the hull and slow it down a bit. The difference is perceptible.

In general I use a combination of motor trim and tabs to correct list. I have yet to use both tabs to actively try to bring the bow down.

Regarding tab installation, I think the advice to mount them 3/8" above the hull plane is good. My tabs were installed almost flush or maybe 1/8" above the V hull, but (like John's Outre) are an inch and a half above the sponsons.

posted 10-04-2005 10:14 AM ET (US)            

Traveling eastbound across Puget Sound from Bainbridge Island to Seattle the wind was stiffly blowing out of the south at 18 knots, thus the wind was coming from starboard where I am standing. The boat will always lean into the wind.

Even when I moved into the companionway to steer with my right hand so I could see past one peeled back corner of the Mills windshield (it was dark and raining) the difference in weight distribution is negligible.

Without trim tabs the hull would have been riding on one side of its V and slamming into each and every wave, big or small. A very punishing ride.

So, as both Peter and Andy point out, if you're onboard by yourself, what are you going to do?

I was never a fan of trim tabs and was actually a bit disappointed that the boat I recently bought had them because they seemed like a lot of extra complication I didn't need. It is now obvious to me that they are a necessity on the Revenge 25.

The 25s do have the huge advantage of accommodating trim tabs without ANY visible clutter. Because of the stern storage compartments, one cannot tell from the inside of the boat that it is equipped with trim tabs. Everything is hidden and out of the way. Only the switch on the dash and the tabs themselves on the transom are visible.

posted 10-04-2005 09:26 PM ET (US)            

I've been using them exclusively (instead of motor trim) to adjust her attitude bow to stern. Tom, can you say more about the Revenge models not needing help in keeping the bow down? I often use my tabs for this purpose.

posted 10-04-2005 10:20 PM ET (US)            

That surprises me. I can only speculate that you are using your trim tabs when the boat is not fully on plane.

Because your boat is underpowered the motor may be at what seems a normal cruising speed (3000-4000 RPM) but the boat is just sort of mushing along on a semi-plane.

I have found the Revenge 25 to have a minimum planing speed of 20-22 mph. On my boat the motors just do not like to run at speeds less than that. Realistic minimum planing speed for me is motors turning 3150 RPM and the boat traveling through the water at 22 mph. Anything less than that and it on the backside of the power curve. That is it takes MORE power to maintain a SLOWER speed.