Cast-Away Posted March 26, 2009 Report Share Posted March 26, 2009 Has anyone here ever had their motor lowered on the transom to help with planing or boat balance? I have a bench seat across the back of the boat and when I have a few adults back there, the boat porpoises a bit and the trim is as far down as it can go, so I thought that lowering the motor might help with this. Right now the anti-ventilation plate sits about on inch above the bottom of the hull and I was thinking about having the marina lower the motor down one more hole. Feedback would be much appreciated. Link to comment Share on other sites More sharing options...
2 tone z71 Posted March 26, 2009 Report Share Posted March 26, 2009 (edited) where it sits, an inch above is about the norm for optimal performance everyday use,to low you can get alot of steering deflection and unwanted spray,I dunno how big your boat is or what kinda power but a set of Lenco trim tabs made all the differance on my CC Edited March 26, 2009 by North East Shark Link to comment Share on other sites More sharing options...
Cast-Away Posted March 26, 2009 Author Report Share Posted March 26, 2009 It is a 17 foot Legend with a 75 4 stroke Merc on the back. Link to comment Share on other sites More sharing options...
hirk Posted March 26, 2009 Report Share Posted March 26, 2009 Put a fin on your cavatation plate,it will carry a load better at low speeds without porpoising and improve hole shot.It's porpoising because it's stern heavy when your loaded. Link to comment Share on other sites More sharing options...
ohhenrygsr Posted March 26, 2009 Report Share Posted March 26, 2009 Lowering your motor below the recommended Boat line will cause excessive drag and lower your speed overall. In general your boat won't run right. I would do what Hirk is saying put a set of fins on Link to comment Share on other sites More sharing options...
MuskieWannabe Posted March 26, 2009 Report Share Posted March 26, 2009 I'm actually having my motor raised up as as I type....If the motor is too low the exhaust will sometimes suck in a bit of water. I foudn that if out by myself, in a tiller, that after 5 or 6 hours of water splashing at the back of the motor it would sputter and spit a little bit. After talking to my mechanic and testing a few things we realized that after a few hours of water hitting my exhaust port, because the motor was too low, it would cause the motor to not run so great. My exhaust was too close to the waterline when sitting idle so we're lifting it up a little bit to give it more breathing room. No doubt it will fix my problem! Cheers! Link to comment Share on other sites More sharing options...
Terry Posted March 26, 2009 Report Share Posted March 26, 2009 I find that most motors need to be raised not lowered I also have seen porpoising from being too low the motor wants to rise to it`s happy place, lifting the boat too high in the water, then doesn`t have the power to maintain the height, wieght so the front of the boat goes up and down when you raise the motor it doesn`t need to lift the boat as high give a more stable ride Link to comment Share on other sites More sharing options...
gdelongchamp Posted March 27, 2009 Report Share Posted March 27, 2009 On a light boat (16' alum) if the boat bunny hops across the water the problem is often solved by putting extra weight in the front of the boat such as a spare tire. Perhaps shifting your passengers around and putting a heavier person in the bow could alleviate the problem. More experimenting may be required before you make adjustments on the transom end of the boat. Link to comment Share on other sites More sharing options...
irishfield Posted March 27, 2009 Report Share Posted March 27, 2009 (edited) Castaway... is there a manual stop on the motor that you can move to get it to trim lower??? (there's a pin on both my 9.9 pro kicker with power trim ) I took the time to get a pin for the old 9.8 merc in the boat house when I bought the camp in Temagami. Then I put it on the boat to find with the pin in the lowest hole the motor wasn't low enough and it porpoised. Removing pin and letting it go all the way down.. perfect. Edited March 27, 2009 by irishfield Link to comment Share on other sites More sharing options...
Cast-Away Posted March 27, 2009 Author Report Share Posted March 27, 2009 No it is power trim Wayne. It is only a problem a few times per year when I have extra people on board and the marina wants $100 to $150 to do it, so if I am not happy, then it will cost me $200 to $300. When I have 4 people in the boat it is not a problem. Link to comment Share on other sites More sharing options...
irishfield Posted March 27, 2009 Report Share Posted March 27, 2009 Yah I know it's power trim... look at each side for stop lugs or a pin.. maybe it can go lower. Link to comment Share on other sites More sharing options...
hirk Posted March 27, 2009 Report Share Posted March 27, 2009 Castaway,unless it porpoises all the time regardless of load which indicates a basic set-up problem ie. engine height and or setback then adjusting height won't fix it.Does it cavitate outta the hole or on moderate turns?If not and it runs good when your not stearn heavy then your setup is good,you just need to make allowances for when your stern heavy,either run a fin or as stated put more weight up front to counter balance. Link to comment Share on other sites More sharing options...
Tybo Posted March 27, 2009 Report Share Posted March 27, 2009 Change the prop. If you still have the aluminum prop on. it is flexing to much making the boat porpoise. Link to comment Share on other sites More sharing options...
BITEME Posted March 27, 2009 Report Share Posted March 27, 2009 Put a fin on it it will fix your problem yes they are that good Link to comment Share on other sites More sharing options...
Bernie Posted March 27, 2009 Report Share Posted March 27, 2009 (edited) Porpoising can be caused by a few different things. Better to porpoise than plow. It's easier to repair/solve. As mentioned before too much weight to the rear, an engine trimmed too high or a hull that is too curved can also cause this issue. A fin mounted on the lower unit is the easiest to install and will more than likely cure your issue. This will also adjust itself with the engine trim. Another option is to mount trim tabs on the transom. The ultimate would be to have power adjustable trim tabs. These will also level your boat in a side wind or uneven side loads. Just as a side note I mentioned plowing. This is generally caused by excessive negative trim or a hull with a "hook" or concaved. This pulls the nose down and causes the boat to plow water. This creates poor handling, loss of speed and poor fuel economy. A hooked hull is difficult to overcome but sometimes a speciality propeller can help. Edited March 27, 2009 by Bernie Link to comment Share on other sites More sharing options...
2 tone z71 Posted March 27, 2009 Report Share Posted March 27, 2009 a set of aluminum transom shims might help,they will help negative/positive trim dont matter all depends on which way you install them ,I put a set on a Boston Whaler Dauntless last season and they heped alot,and not noticeable like that big ugly whale tail ewwwwww Link to comment Share on other sites More sharing options...
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