smboudreaux Posted August 10, 2018 Report Share Posted August 10, 2018 hey guys. i'm having issues with speed and front heavy ride on my 98 Hewes Light Tackle 20. Its powered by a 98 200 yamaha vmax. top speed is 43-44 at 5800 rpm. from what i've read guys with the same setups run in the mid to upper 50s. I started thinking maybe prop and that research brought me to jack plate height. Investigating my motor i height i discovered motor was 1-1/2" low base on the 3-1/2" from bottom of the hull to the center line of the prop method. with the motor in this position that cavitation plate is roughly 4" above the bottom of the hull. can anyone shed some light on this problem? i was headed out to run it but the weather got me. Link to comment Share on other sites More sharing options...
HoneyB Posted August 10, 2018 Report Share Posted August 10, 2018 Lifting your motor one inch will not get you 8 to 10 mph. I would be looking for a slipping hub or a fuel restriction. Possibly even a fouled out plug or even a dead coil. Link to comment Share on other sites More sharing options...
smboudreaux Posted August 10, 2018 Author Report Share Posted August 10, 2018 Roger that. Appreciate the insight. Wouldn't a fuel issue or spark issue have some other symptoms with it? It seems if it was fuel I wouldn't make the power to turn the rpms. Spark seems it should have a rough idle or miss. I'm guessing here. New with trouble shooting outboard. Trying to apply vehicle mechanics Link to comment Share on other sites More sharing options...
dabear Posted August 10, 2018 Report Share Posted August 10, 2018 28 minutes ago, HoneyB said: Lifting your motor one inch will not get you 8 to 10 mph. I would be looking for a slipping hub or a fuel restriction. Possibly even a fouled out plug or even a dead coil. That’s a lot of a speed gain , What about lifting it 2 inches would that speed double ? Are these real world numbers from your own testing ? Link to comment Share on other sites More sharing options...
HoneyB Posted August 10, 2018 Report Share Posted August 10, 2018 20 minutes ago, dabear said: That’s a lot of a speed gain , What about lifting it 2 inches would that speed double ? Are these real world numbers from your own testing ? I think you missed my point. I said raising the motor one inch will NOT get him the speed he thinks he is missing which looks to be 8 to 10 mph. I think the motor is struggling or he is not getting the power to the ground(water). Slipping hub or not enough fuel or fire. I had a 150 optimax that lost a coil on two separate occasions. The only way I knew it was not fireing was top speed. The motor ran great idled great jumped the 19 foot pioneer on plane. The only indication that I had a problem was WOT speed was low to mid 40’s rather than 50 mph Link to comment Share on other sites More sharing options...
smboudreaux Posted August 10, 2018 Author Report Share Posted August 10, 2018 Ok so it sounds like the missing speed is not from motor height. So I'll keep hunting that problem. But.... back to the original question. Which method would be better for getting motor height? 3.5" from keel to prop center line or cavitation plate 1.5" above the keel? Link to comment Share on other sites More sharing options...
dabear Posted August 10, 2018 Report Share Posted August 10, 2018 Ok HoneyB your right I did miss the point that you where making my mistake , Link to comment Share on other sites More sharing options...
HoneyB Posted August 10, 2018 Report Share Posted August 10, 2018 I have always used anti cave plate 1 to 1.5 above as a starting point .. then raise a hole or two if that 1 To 2 mph gain was being sought. Trust me once you got to high the boat will let you know Link to comment Share on other sites More sharing options...
polliwog Posted August 18, 2018 Report Share Posted August 18, 2018 I have your boat,but with a 150 Yamaha VMAX, I don't get more than 45 at WOT, but I have a painted bottom and 50 less HP. I would think your WOT should be about 50, These boats are heavy and bow heavy especially with a troller on the front.. I'm at the stage in life where 35-40 cruising speed is just fine LOL. Link to comment Share on other sites More sharing options...
geeviam Posted August 18, 2018 Report Share Posted August 18, 2018 On 8/10/2018 at 3:08 PM, smboudreaux said: Ok so it sounds like the missing speed is not from motor height. So I'll keep hunting that problem. But.... back to the original question. Which method would be better for getting motor height? 3.5" from keel to prop center line or cavitation plate 1.5" above the keel? IMO, with all the variables (setback, transom pocket, jack plate, vee vs pad, etc), the best way to know if your motor is running at the correct height is to let your co-pilot take the wheel while running at speed, motor trimmed level (not tucked in), jack plate all the way down, and you look down where the motor meets the water. The underside of the AV plate on the lower unit should be riding right on the surface of the water, with no air gap. From that point, you should be able to tuck the motor in for better grip in turns, and raise the JP and/or trim-tilt for top performance running a straight line. To answer your question... the experts say that the distance between the hull pad/keel and the prop shaft center-line should be 3 1/2", when setting up a jack plate. Mine is a little more than that, but when you have the ability to raise a jack plate up to 5" higher, it doesn't seem to be all that important. Link to comment Share on other sites More sharing options...
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