Trim Tab adjustment?

[69 Shopbuilt]

Another dumb question. So dumb I'm not sure how to state it. How far up should the trim tab be at the upper most notch? How low? I borrowed a GPS and was making some runs before I change props. Went with it all the way up first, then tried with it all the way down, lost considerable speed. And got squirrelly, especially when I let off the throttle. Maybe it should be adjusted up some overall? Anybody got any info, would appreciate your help.

[Flatmvn]

I will take a shot at this. First what type of system do you have, Pedal with over ride, pedal only or override only. From the way you describe it you have an override handle only. Here is a pick of a duel pedal assembly with a override handle.

http://i209.photobucket.com/albums/bb16/flatmvn/Rush/DSC_0010.jpg

With the handle in the forward or up position that is when you boat will run its loosest if you put the override in the back or down position it will make the boat stay down in the water more and sometimes it will cause it to Bow steer which is what it sounds like you are doing. This equates to more boat in the water the slower it is going to be. The less boat in the water the faster it is going to be.

[RiverRacer]

With the handle all the way up the plates should be free so they don't bind on the trailer. Pull the handle two notches back and set your plates to it's proper riding attitude at speed, then use the down pedal to adjust to water conditions!.. But if the power, gear and prop combo and boat setup is not right this won't mean anything anyways!...

[69 Shopbuilt]

I only have the override handle. Still working on getting it all set up. Trying another prop today.

[RiverRacer]

Need to put a down pedal in there!.

[gfinishline]

I'd like to comment, but I haven't read anything about what the boat has for equipment, balance, prop......

[69 Shopbuilt]

What's the down pedal's purpose?
Need to put a down pedal in there!.

[RiverRacer]

What's the down pedal's purpose?

To push the plate down with your foot while driving!..

[Terrible toy]

To push the plate down with your foot while driving!..

Might I add, very important to life and limb.:D 69 Shopbuilt give gfinishline his needed info, he's da man.

[69 Shopbuilt]

It's just an old 69 flatbottom with a stock SBC truck engine, auto tranny, top loader casale, 12*, 8%, 12 1/2 x 13 three blade. Since I got this prop it turns 4100 at 47 mph tops. Of course I'd like more speed but can't afford it. It's fine for what we use it for, family ski boat. The new prop got rid of the vibration problem and I'm quite happy with the boat. It is very stable and handles really well.

Dave


I'd like to comment, but I haven't read anything about what the boat has for equipment, balance, prop......

[gfinishline]

OK, I'll bite. What is the shaft angle, weight, est. power? Looking at 8% gears and 13 pitch, I would say that before you adjust your cavitation plates look at some valve springs or a tune up! When you get the motor running up to a reasonable level, then we can look at your prop. After that is corrected, we can then look at "plate settings", and prop "placement', either forward or back from it's present position. This is where I would start if it were my boat.

[RiverRacer]

This should get very interesting and educational!..

[69 Shopbuilt]

I'm not trying to be a smartass here fellows. I would think it's obvious by now that I don't know squat about these boats. I have learned more in the short time since I joined this forum than I ever knew about them before. There seems to be an abundance of information here and I am trying to benefit from your expertise. The pitch is 12*. I have no idea how much it weighs, the stock sbc only puts out around 200 horses, at best. I realize now that at the speed I get, I don't need to worry about the plate settings.


OK, I'll bite. What is the shaft angle, weight, est. power? Looking at 8% gears and 13 pitch, I would say that before you adjust your cavitation plates look at some valve springs or a tune up! When you get the motor running up to a reasonable level, then we can look at your prop. After that is corrected, we can then look at "plate settings", and prop "placement', either forward or back from it's present position. This is where I would start if it were my boat.

[AquaCraft]

It's just an old 69 flatbottom with a stock SBC truck engine, auto tranny, top loader casale, 12*, 8%, 12 1/2 x 13 three blade. Since I got this prop it turns 4100 at 47 mph tops. Of course I'd like more speed but can't afford it. It's fine for what we use it for, family ski boat. The new prop got rid of the vibration problem and I'm quite happy with the boat. It is very stable and handles really well.

Dave

Hi Dave,

I am glad to hear that changing props got rid of the vibration problem. 4100 RPM, 47 MPH, very stable, handles real well; this sounds like that SBC truck motor is performing right where it should in your boat.

You are right, for the speed you (and I) go; put the plate "down" a bit to plane at a low speed 'pulling the kids, 'sneak the plate "up" a bit to lift the bow for more top speed.

If you poke back through some of the old threads you will find good help on initial adjustment of the plate to a "neutral" position.

If you can't find the threads; PM me and I will help you out.

AquaCraft

[RiverRacer]

I realize now that at the speed I get, I don't need to worry about the plate settings.

That is correct, just put the plate where it will ride smooth cruising and forget about it!..

[69 Shopbuilt]

Found the old threads, thanks for the guidance. Seems like mine has been set to where it is a little bit down even in the uppermost notch. I can nail it from a dead stop and it will bite and go. I'm gonna try to adjust it like in the threads and give it a try.

BTW, I tried it with the handle all the way down, it plowed hard and when I let off the gas, it went hard to the left and I got wet.

Dave


Hi Dave,

I am glad to hear that changing props got rid of the vibration problem. 4100 RPM, 47 MPH, very stable, handles real well; this sounds like that SBC truck motor is performing right where it should in your boat.

You are right, for the speed you (and I) go; put the plate "down" a bit to plane at a low speed 'pulling the kids, 'sneak the plate "up" a bit to lift the bow for more top speed.

If you poke back through some of the old threads you will find good help on initial adjustment of the plate to a "neutral" position.

If you can't find the threads; PM me and I will help you out.

AquaCraft

[gfinishline]

I would look at your "12 1/2 prop" I feel it's too large for the boat weight. Can you try/borrow some other props? I like 11" for 18' 6" and under hulls, as far as bronze 3 blades go. With 8% gears, I'll bet an 11" X 14 pitch would really run well for you. (at your power level) Then it's the old "nickles in the coupler" game. Try setting your control on the third notch from the top, and setting the plates LEVEL with the hull bottom. Then adjust the last outside right end turnbuckle/ plate at 1/8" down. (below hull bottom line). Run the boat. If you can move the handle up to the SECOND notch and the boat doesn't bounce, go up to the first notch. If the boat bounces (at top speed) with the control on the third notch, install THREE NICKLES in the shaft coupler. Repeat the test, adjust NICKLES as the nose (deck) rises or falls down, at top speeds. You want the boat to run with minimal "up and down" at ONE NOTCH down from the top, without having too much hull in the water (excess drag). The right end is adjusted down to counter act the (flywheel forward) torque to the hull.

[69 Shopbuilt]

Thanks gf,
This is the kind of info/advise I need. Adjusted the plate, tried it yesterday. Got a little front end lift but apparently got the right end down a little too far. It leaned to the left side pretty bad. Got to find some hardware for the adjusting hardware. Bushings worn out/ gone, turnbuckles siezed up, set screws missing, stripped out etc. Will update when I get some more to post.
Dave

[69 Shopbuilt]

Forgot about the props suggestion. I am checking around, but not much available right now. Will try the nickels when I get some of this other mess straightened out.

[gfinishline]

Please don't equate "steering pull" with "hull angle", it's two different animals. Keep up the progress/learning, you will go faster!

[69 Shopbuilt]

Please don't equate "steering pull" with "hull angle", it's two different animals. Keep up the progress/learning, you will go faster!

Not sure which term is applicable. The boat rides like as if it were sitting still with a couple hundred pounds more weight on the port side. I adjusted the plate a little and it isn't as bad, so I guess I'm on the right track. Get that worked out I want to try your nickels tip. Looks like I am gonna need a different prop as well. Picked up three-four hundred rpm when I adjusted the plate. It was down about 1/2 below the hull.

Appreciate your help.

Dave

[gfinishline]

Did you use a "straight edge" on the bottom of the hull and plates? (front to rear) This will set everything up to LEVEL with the BOAT BOTTOM, if you have your control handle forward to the SECOND NOTCH from the front. (away from you) Then just turn the right (starboard) outside (only) last turnbuckle down 1/2 of a turn (3 flats). Then run the boat and report. I still don't like your "airplane propeller". TOO BIG!

[gfinishline]

I just looked at your photos and in #4 you are driving (right to left) and the entire keel is wet. Were you at any kind of speed? Please do ONLY ONE CHANGE AT A TIME, and we will help you. The props in your photos are the kind that 'lift the tail', so don't move the prop (nickles) just yet. Let's get the plates up to where they need to be.

[69 Shopbuilt]

Did you use a "straight edge" on the bottom of the hull and plates? (front to rear) This will set everything up to LEVEL with the BOAT BOTTOM, if you have your control handle forward to the SECOND NOTCH from the front. (away from you) Then just turn the right (starboard) outside (only) last turnbuckle down 1/2 of a turn (3 flats). Then run the boat and report. I still don't like your "airplane propeller". TOO BIG!

That's what I did except I had the last one too far down down. Got that adjusted, running level again. Made a hell of a difference, less drag, picked up some speed and rpm. Running too fast (rpm) for the stock sbc again. The prop I have on it now is definitely better than the old one but obviously not right yet. I'm looking around for another one to try, but no luck yet. Not financially able to buy new ones just to try out.

Dave

[69 Shopbuilt]

I just looked at your photos and in #4 you are driving (right to left) and the entire keel is wet. Were you at any kind of speed? Please do ONLY ONE CHANGE AT A TIME, and we will help you. The props in your photos are the kind that 'lift the tail', so don't move the prop (nickles) just yet. Let's get the plates up to where they need to be.

I was not up to speed in that pic. Will see if I can get one with it running and post it. Yeah I learned a long time ago not to change but one thing at the time. Only way to know if you're doing good. I know you can't help me a lot with the little info I have on the boat, but I do appreciate what you help me with. Do you have any idea what prop I need to try? I've been tring to find a way to get the boat weighed so I could at least have that much to go on. I know it is heavy, built real solid. I can stand on the front deck and it doesn't give a bit.

[gfinishline]

Did we talk about gears? If you don't know what it has, try this. Put a mark on the input flange (@12 o'clock) and the same kind of mark on the coupler (@ 12 o'clock) (load the clutch to one side) Turn the input shaft TEN TIMES, while counting how many times the output shaft turns. If the top turns 10 times and the bottom turns 'aall -most 11 times, you have 9's. A little more than 11 times would be 12's..... and so on. If you are 'running out of motor RPMs', I would look at a set of new valve springs. Usually stock engines have weak springs, and it would be "money in the bank" to avoid 'piston to valve contact". If you have LOWER than 12% gears, I would try an 11" X 15 two blade. If you have HIGHER than 12% gears, try a 10 3/4 X 15 two blade. Is the boat "stuck in the water" as it sits? Does it bounce or hop at all? Now that you have the plates close.

[69 Shopbuilt]

Did we talk about gears? If you don't know what it has, try this. Put a mark on the input flange (@12 o'clock) and the same kind of mark on the coupler (@ 12 o'clock) (load the clutch to one side) Turn the input shaft TEN TIMES, while counting how many times the output shaft turns. If the top turns 10 times and the bottom turns 'aall -most 11 times, you have 9's. A little more than 11 times would be 12's..... and so on. If you are 'running out of motor RPMs', I would look at a set of new valve springs. Usually stock engines have weak springs, and it would be "money in the bank" to avoid 'piston to valve contact". If you have LOWER than 12% gears, I would try an 11" X 15 two blade. If you have HIGHER than 12% gears, try a 10 3/4 X 15 two blade. Is the boat "stuck in the water" as it sits? Does it bounce or hop at all? Now that you have the plates close.

Got the plates as close as possible with a couple of siezed turnbuckles. I took it out today for another trial. I set the plate with it in the next to highest notch. I started out with it in the middle notch, only got 42.3mph, was a rough ride, sits too low in the water. Raised it to the next higher notch, got up tp 47.3, smooth ride, side splash back close to rear of boat. Raised it to the highest notch, got 47.9, but it bounced pretty bad. Was alone so no pics yet, but maybe this will help.

Will check the gears as per your instructions next and check on valve springs.

Thanks,

Dave

[hm66Howard]

I don't want to jack shopbuilts thread, just looking for more info. I've been following this thread with great interest 'cause I've never played around with the plates on the Howard. I just put them back on in the same places they came off. The boat handles well and tracks straight. She does hop with the control in the top positions. Eyeballing down the edge of the plate it isn't straight. It has a little "wowie" in it on the right side. I'm just wondering if they're not set optimum. I also noticed now with the ski tow and pulling the kids around, it seems to be very tail heavy. Maybe it's just 'cause we're not going fast enough to plane but, she digs a trench through the water.
My questions are:

1) How are you guys pulling your boats back on the trailer to get your straight edges on the bottom? How do you get it back up on the trailer?

2) Once I've set the control in the third location from the front, plates flush, left end 1/16" up, right end 1/16" down, what am I looking and feeling for to "fine tune"? Some examples would be great with the corresponding action to take with the plate turnbuckles. You know like, "if the boat does this or acts this way, you want to do this."

Thanks to all for your info and knowledge. :D:D:D

[RiverRacer]

If you have an engine hoist just hook it up on the motor and take up enough weight to slide it back and forth, if you don't have one take it to the launch ramp and float it!..

Don't know what the "wowie" means, but both plates should be the same put a staright edge from the center out and both sides need to be the same!. Keep your corners the same, center flush with the bottom unless you have a rocker, from the center to the corner put a 1/16-1/8 gull on both sides and go from there!..

[hm66Howard]

Wowie was just a colorful term for not straight. It looks like out of the eight turn buckles, the 3rd turn buckle in on the right side is longer then the two on each side of it putting a very slight dip in the plate. I want to start from scratch and set the plate to your instructions. What do I do after that for "fine tuning" to make it perfect? :)

[RiverRacer]

Wowie was just a colorful term for not straight. It looks like out of the eight turn buckles, the 3rd turn buckle in on the right side is longer then the two on each side of it putting a very slight dip in the plate. I want to start from scratch and set the plate to your instructions. What do I do after that for "fine tuning" to make it perfect? :)

Ok gotcha, if that turnbuckle is too long and can't get enough adjustment you'll need to shorten it!.. "Fine Tuning", you'll have to try it first and see what it does!...

[hm66Howard]

Art, when you refer to hook and rocker, are you speaking fore and aft or side to side? From center to side of the transom there is 7/16" difference. And by "gull", do you mean up or down? Just want to clarify what I'm looking for when I slide the boat back to do this.

[RiverRacer]

Fore and aft, put a straight edge along the strut from at least 3' forward of the strut, if I remember right it should be flat all the way back!..

[hm66Howard]

Thanks Art. I'm getting ready to do this this week maybe. Just one more clarification. By "gull" you mean "up" right? Thanks :)

[RiverRacer]

Thanks Art. I'm getting ready to do this this week maybe. Just one more clarification. By "gull" you mean "up" right? Thanks :)

Yep!.....;)

[hm66Howard]

Thank you sir. Your the man! :D:D:D

[RiverRacer]

Thank you sir. Your the man! :D:D:D

Anytime amigo!.:D