Jackplate/trim tab setup questions...

[vissertrades]

Hi all!<br /><br />I've got some boat setup questions so here's a little background info: <br /><br />Boat is Smokercraft 15.5' (aluminum) center console (maybe 600Lb) modified V. Engine is a 1995 Johnson 50 (two cylinder). I put a Detwiler 6" jackplate on it last winter and I'm dialing it in now. Prop is a 11-3/4x17 Stiletto. Motor is mounted as low as it can be and AV plate is about 1" above the pad. I have a water pressure gauge installed too. The boat also has Smart Tabs installed. Here are the results of recent testing:<br /><br />Current height. 35/36 Mph. 5600-5700 rpm. Can trim way out before prop slips but boat will porpoise fairly quickly and I needed to trim in. Water pressure 18-20psi.<br /><br />1/4" up from where its at now I hit 36/37 Mph at 5800rpm trimmed just under where prop slips. Boat eventaully started porpoising under light loading and empty bow when trimmed out just before prop slip. Water pressure 18-20psi.<br /><br />1/2" up speed was slightly less. Rpm was in the same range. No porpoising but prop would blow out with less trim. Water pressure the same.<br /><br />1" up and speed decreased. Rpm and water pressure about the same as 1/2". Prop would break loose VERY easily. <br /><br />I have not adjusted the Smart Tabs and they are at the mid/lightest setting. I *think* i'm real close to the ideal setting but don't like the porpoising. I can adjust the tabs lighter or heavier. <br /> <br />So my question is:<br /><br />1. Based on the above where do you think the proper engine height is?<br /><br />2. Should I loose (or lighten) the Tabs to see if I can get past the porpoising and carry the bow?<br /><br />3. Use the tabs to force the bow down via lifting the stearn?<br /><br />4. Find a way to lower engine more?<br /><br />I'll try all of these anyway but I'm just looking for some experianced advice. I'm surprised how quickly the prop slipped when raised only 1". <br /><br />Thanks!

 

[LubeDude]

Re: Jackplate/trim tab setup questions...

Im sure Nautijohn will show up eventually, but i would say keep it where it is, and ad a little more preasure to the tabs.<br />---------------------------------- <br />

 

[Mercathode]

Re: Jackplate/trim tab setup questions...

Hi Piet<br />I am not sure that a package like this will yield a constant bow high run. Your hull design along with a small prop diameter may not be able to give you temendous bow lift. You may set the tabs where they will bite just before she poroises. As for as speed it appears you got a good running 50!<br />LW

 

[Jdeagro]

Re: Jackplate/trim tab setup questions...

It is noce to know that some of our customers are getting to know how to adjsut these Smart Tabs. makes me very pleased.<br /><br />Hi Pete;<br /><br />I would also suggest that you increase the tab pressure a bit ( move the Actuator up and away from the plate bracket base about 1/2 to 3/4"), and put the jack plate back to the "current" position. Sounds as though the prop is about to come out of the water at 1/2". The extra pressure on the tabs may raise the stern enough while also eliminating the porpoising.

 

[vissertrades]

Re: Jackplate/trim tab setup questions...

Thanks for all the comments Guys! I'll play with the TT settings. John, FYI I'm using the 40# actuators set near the weakest setting. I'll keep the motor height where it is now as prop seems to bite best. Hopefully increaseing tab pressure wont scrub speed at this point. I'm hoping that with the motor in the current setting with the TT's tweaked to control porpoising and the additional stern lift I just may get some more R's. In the current setting now I really had to back off the trim to calm the boat down. I really think I've sqeezed all I can out of this rig. Maybe it's time to step up to a Skeeter with a 225? It's been really fun dialing this boat in and I may even FISH soon (that would make the JR's happy!). God help me if I loose one of those trim tabs as I'll be sitting on a finely balanced teeter totter going 36 Mph!

 

[Jdeagro]

Re: Jackplate/trim tab setup questions...

Piet;<br /><br />You will not get that kind of reaction at speed - not to worry. Besides they do not fail that quickly.

 

[BillP]

Re: Jackplate/trim tab setup questions...

Sometimes just uneven weight will cause the boat to porpoise. I had a 20' vee bottom flats boat that would porpoise if I sat too far one side or the other...it had cockpit adjustable tabs, jackplate, low water pickup and h20 psi gauge. Try shifting weight around and see if it helps. Then do the tabs. But your speed isn't that bad considering the hp/weight.<br /><br />My setup with a Bob's machine hyd jackplate ran fastest with 1/2 of the 4 blade prop hub out of the water. The motor trimmed level (not out)and the jplate raised until the h20 pressure dropped. Tabs worked best trimmed high with zero resistance.