Trim tab questions

[Undersoul02]

So my dad wants to get trim tabs put on his 21 ft California Cool. The boat has a porpoising problem unless everyone in the boat is sitting driver seat or forward. Trimming the outdrive won't fix the problem. We've never had them on any of the boats we've owned so we aren't sure with how to proceed.

My questions:
Should he go with hydraulic or electric? Or does it matter?
Is there a preferred brand?
Is it something we should do on our own or have a shop do? If shop, is there one near Long Beach CA that would be recommended?

Thanks for any help and here is a couple pictures of the boat.

Thanks - Ryan

 

[ka0tyk]

lenco or bennett trim tabs would be the best bet. biggest difference is that if growth or salt gets onto the ram, the hydraulic only requires a new oring, fluid, etc to get back into shape, whereas a seal failure on an electric ram requires a full replacement. hydraulic are gonna last longer, but require more installation work with hoses and a pump, also more costly up front. i dont see why you couldnt do electric tabs on that size freshwater boat and be gravy. installation isnt too tough if you can use a drill, screwdriver, and silicone.

[video=youtube;cV2BKm1s0iQ]https://www.youtube.com/watch?v=cV2BKm1s0iQ[/video]

 

[AzGeo]

what is that doing for you now ? If you remove it, what will the boat do ?

You can keep adding on more drag, but I feel that there may be a better way to solve your problem .

You could add 'fixed plates' to extend the lifting surfaces, but how long and wide will be required to cure the problem ?

When I have rigged hulls that had 0, 9, 12 degree transom angles, I always used a '5 degree wedge' behind the transom piece to the hull . This gives 5 degrees more DOWN on the prop thrust, does not add drag, and also gives great 'mid speed control' and still has plenty of UP trim for top end .

I hate driving I/O boats that require the use of 'tabs and drives' just to get onto plane .

Every (old style) Howard 21' I rigged with an I/O, had the 5 degree drive wedge, and none of them required any plates at any time .

Don't add drag, and this advise coming from a guy who made a living fabricating cavitation plates and hardware .

 

[ka0tyk]

what is that doing for you now ? If you remove it, what will the boat do ?

You can keep adding on more drag, but I feel that there may be a better way to solve your problem .

You could add 'fixed plates' to extend the lifting surfaces, but how long and wide will be required to cure the problem ?

When I have rigged hulls that had 0, 9, 12 degree transom angles, I always used a '5 degree wedge' behind the transom piece to the hull . This gives 5 degrees more DOWN on the prop thrust, does not add drag, and also gives great 'mid speed control' and still has plenty of UP trim for top end .

I hate driving I/O boats that require the use of 'tabs and drives' just to get onto plane .

Every (old style) Howard 21' I rigged with an I/O, had the 5 degree drive wedge, and none of them required any plates at any time .

Don't add drag, and this advise coming from a guy who made a living fabricating cavitation plates and hardware .

if you add 5 degrees to the transom mount, wouldnt that change the angle of the shaft and thus require the motor to sit higher as well? i cant find anything online about a transom assembly wedge...

 

[ka0tyk]

ps what happened to your skeg? that cant help with handling either... i see stainless prop and a fin, what prop you running and have you tried other props?

 

[BigSteve]

Az geo is correct when it comes to set up.
A properly set up boat solves a lot of problems

Lots of boats sit on piss poor designed trailers that screw up a fine boat
I would start with a basic check of the hulls last 3 ft with a straight edge and a light
Looking for a hook. A speed and trim killer

Putting on the correct prop for load and conditions minimize issues

The last thing you go to is tabs !
They do work the hydraulic is the better way to go
I have used the Lenco electric with the led indicator and auto retract good for a two to three seasons.

We do find special uses for trim tabs on over propped tunnel boats with o/b twins that can't get the extra neg engine trim we run them over the tunnels to eliminate drag at speed

 

[AzGeo]

the motor height/angle does change, but the whole boat will run much better for it . Low speeds will be very controllable, and upper speeds will also be much smoother .

I have found that 'placing the thrust in the optimal position', always produces the best results .

I have been designing, fabricating, and installing ultra high performance trim tabs/cavitation plates, along with re-shaping hundreds of racing boat bottoms, over the decades .

IMO, adding adjustable 'tabs' or even static plates is NEVER close to the performance gains achieved when the original problem with the set up is solved .

Look, I make money on cavitation plates and all their controls . I ALWAYS tell my JET customers to "first go with a Place Diverter", then tell me what you also want for your personal 'feel' when racing your boat .

IMO, controlling thrust is always better than adding more drag .............

 

[ka0tyk]

only reason i ask is because in my 21 bahner with a ss mirage 23p prop the boat would run wet at speed on that last 1/3 of the boat... but no matter how much i trimmed down i could never get the nose down to "cut" through chop. i was always having to go over it and most of the time that involved some pretty hard bumps and having to slow down to avoid kidney failure. i ended up putting some older kiekhaefer trim tabs on it. fully up it allowed the boat to drive as usual and i really didnt lose any speed... but when it got bumpy i could push the nose down a little and the boat rode a THOUSAND times better than it ever did. sure you'd feel the speed loss but the ride quality was well worth it. i experienced the same thing with the howard 220 this weekend when driving it in the afternoon windy chop on lake mohave. also it was nice with the deep vee being able to trim from side to side as i had a beefy passenger sitting on one side.

it makes me wonder about getting a set of lenco/bennett's for the warlock once its put together...

 

[BigSteve]

only reason i ask is because in my 21 bahner with a ss mirage 23p prop the boat would run wet at speed on that last 1/3 of the boat... but no matter how much i trimmed down i could never get the nose down to "cut" through chop. i was always having to go over it and most of the time that involved some pretty hard bumps and having to slow down to avoid kidney failure. i ended up putting some older kiekhaefer trim tabs on it. fully up it allowed the boat to drive as usual and i really didnt lose any speed... but when it got bumpy i could push the nose down a little and the boat rode a THOUSAND times better than it ever did. sure you'd feel the speed loss but the ride quality was well worth it. i experienced the same thing with the howard 220 this weekend when driving it in the afternoon windy chop on lake mohave. also it was nice with the deep vee being able to trim from side to side as i had a beefy passenger sitting on one side.

it makes me wonder about getting a set of lenco/bennett's for the warlock once its put together...[/QUOTe

I think the benefits can out weigh the negatives running movable tabs over the tunnels
The bow rise is almost eliminated at take off and the planing speed is reduced 30%
At speed a slight tap on the tap and the nose drops, nicer ride in a head wind

 

[Undersoul02]

AzGeo - I've never thought about the drive wing and what it might be doing to the ride. The boat came with it on and we've always had the porpoise problem with this boat.

ka0tyk - my pops broke the skeg off last summer and had no effect on the way the boat preformed as far as porpoise. It's always had this problem. He's just finally gotten fed up with it.

Big Steve - I'll check the hull with a straight edge for sure. Like said though the boat always had the problem. As far as props he has 2. Both are stainless. First is a 3 blade 21 pitch and the second is a 5 blade 19 pitch. Both have the same problem. Altho the problem is at different rpm's.

 

[BigSteve]

AzGeo - I've never thought about the drive wing and what it might be doing to the ride. The boat came with it on and we've always had the porpoise problem with this boat.

ka0tyk - my pops broke the skeg off last summer and had no effect on the way the boat preformed as far as porpoise. It's always had this problem. He's just finally gotten fed up with it.

Big Steve - I'll check the hull with a straight edge for sure. Like said though the boat always had the problem. As far as props he has 2. Both are stainless. First is a 3 blade 21 pitch and the second is a 5 blade 19 pitch. Both have the same problem. Altho the problem is at different rpm's.

How much trim do you use at mid range and full throttle operation?
Does the hop ever go away ?
Some hulls will hop a bit at slower speeds and it goes away as the speed picks up and go away and some have mid range trouble zones

Are you fully trimmed down when the boat is hopping

AZGEO has a very valid point on the transom wedge angle !

When our team test drives boats we are always asking ourselves
what is the boat asking for to make it happy !

 

[Undersoul02]

How much trim do you use at mid range and full throttle operation?
Does the hop ever go away ?
Some hulls will hop a bit at slower speeds and it goes away as the speed picks up and go away and some have mid range trouble zones

Are you fully trimmed down when the boat is hopping

AZGEO has a very valid point on the transom wedge angle !

When our team test drives boats we are always asking ourselves
what is the boat asking for to make it happy !

If the boat has 2 people in it, driver and passenger, it doesn't have the problem. We can trim the boat up and down without issue. As soon as we get 4 or more people in the boat it begins to porpoise. The problem begins at low speed, 20 - 25 mph and continues throughout the throttle range even fully trimmed down. The only way we can fix the problem is to have as many people sit in the front of the boat as possible.

I hope that answers what you were asking?

 

[BigSteve]

If the boat has 2 people in it, driver and passenger, it doesn't have the problem. We can trim the boat up and down without issue. As soon as we get 4 or more people in the boat it begins to porpoise. The problem begins at low speed, 20 - 25 mph and continues throughout the throttle range even fully trimmed down. The only way we can fix the problem is to have as many people sit in the front of the boat as possible.

I hope that answers what you were asking?

Your explanation is fine.

I would look for a hook in the hull. Using a long straight edge.
Sitting on trailers tends to screw them up over time and fiberglass shrinkage.
Hooks will cause the nose to stay down and not free up easily
So the driver will over trim to try and free up the boat
The boat breaks free pops the nose and the hook slaps it down
The cycle continues until you overload the nose! Or have the ability to add more neg trim

You may a also have a hull that has known issues I am not familiar with your exact hull.
No matter you take what you got and work with what you got.

Do I add plates and how much fixed or not
Az geo is on point !

Driving at 75 in a twin Daytona is a bitch 70 ok 80 ok
We hit the center tab sometimes in 75 mph river traffic or do the Pomona hop.

 

[Undersoul02]

BigSteve thanks for your information. I'll take this to my dad and see what he wants to do. He's talked about getting ride of this boat and buying something bigger. This might just push him over the edge.

Thanks again everyone!

 

[AzGeo]

It's got a 'jet boat bottom', and the transom is 'west coast' almost straight up and down .

Five more degrees of DOWN TRIM, lifts the tail that should have had strakes under it . (but it's for a jet)

I did/learned on a couple of Howard Brown's 21's and they had a (I think 12 degree) transom with little attack angle built in .

Adding a 'Specialty Marine' 5 degree angle piece, and mounting the motor a little higher, made the boat NOT WANT plates of any kind, while still having a TON of UP TRIM . (big or small blocks)

Today I just machine up a slab of aluminum on my mill .

YES, I am the guy who wants to 'do bottom work', on most every hull I meet . But short of that, my next choice is to 'optimize the thrust vector', and then my last choice would be 'adding more drag' . (tabs-plates)

You know I've been designing and building race cavitation hardware and controls for decades, yet 'adding plates' does not always give the best results .

 

[BigSteve]

YES, I am the guy who wants to 'do bottom work', on most every hull I meet . But short of that, my next choice is to 'optimize the thrust vector', and then my last choice would be 'adding more drag' . (tabs-plates)

You know I've been designing and building race cavitation hardware and controls for decades, yet 'adding plates' does not always give the best results .[/QUOTE]

Getting the bottom is right is a very difficult task and the key to victory !
It took us four times flipping the boat over and modifying to reach the window and optimize the thrust vector
The final result after the work is the boat runs best at neutral trim, racing or cornering, slight neg at speeds over a hundred, the boat is running flat to the water without dragging while minimizing the air entrapment spillage and skimming the pad
The only time I use positive trim is to lift the nose in rough water for a smooth ride!

I would like to have you make a custom set of plates for my boat!
Yes, I want to add drag to my boat !
Actually I want to aid in my boat ability in the hair pin corners at the Parker race
I figure if I can brake harder and get it to heel to port at the bouy
I can save time on the clock

 

[AzGeo]

Would 'tunnel side curtains' help level the straight away speeds (and trim angle) ? Longer rear air traps, to hold up more of the motor weight .

Testing this and my own design of surface drive are why I want to build a tunnel boat . Nothing fancy, just a 'test mule' to work on all the "what if's" .

 

[BigSteve]

Would 'tunnel side curtains' help level the straight away speeds (and trim angle) ? Longer rear air traps, to hold up more of the motor weight .

Testing this and my own design of surface drive are why I want to build a tunnel boat . Nothing fancy, just a 'test mule' to work on all the "what if's" .

Your observations are spot on !
It's all a balancing act, it comes down to speed vs cornering at times

We do a lot of boating in the Delta
Filled with a thousand corners of every type
Tabs can be your friend or enemy
Yes you can gain speed and bow set with tabs
Down side you can float the ass and take way longer to take a set in the corners
We changed the installation to lift up a extra 15 deg to bleed air and regain cornering

The tab arrangement I have in mind uses air pressure from the engine air pump to fill a small storage tank
to activate light weight air brake chambers pushing the plates down,a return spring to lift the plate up plus 15 deg. A turn signal style trim switch trips the relays and 12 v air solenoids tap up the first solenoid and adjustable air pressure regulator brings the plate level
Tab down on switch to get more plate by setting a second adjustable regulator at a higher pressure
A foot switch resets the relays and lifts the tabs to plus 15 deg a second floor switch trips
A third solenoid for racing Parkers hair pins , the starboard plate is activated to heal the boat over at the buoy

Simple go fast , brake hard and turn left !