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ContinuousWave: Whaler Performance
Raising motor up?
|Author||Topic: Raising motor up?|
posted 05-16-2004 07:25 PM ET (US)
I am considering moving my outboard up as a effort to improve overall handling. I have a Johnson 150 on an 18 Outrage. It was fine until I put a 4 stroke 8 hp kicker motor on it and it porposes at almost any trim angle except all the way down. I have put on a hydrofoil which has helped some, but I have lost most ability to trim down further in choppy water. That kicker plus an extra battery in the rear along with the main battery have affect the trim of the boat that much.
I want to keep the kicker in the event of a breakdown since here in Utah tow in services aren't exactly covered well by a radio call.
I know that moving batteries foward would help. I want to preserve room in the center however.
My Johnson has 4 mounting holes. I am currently on the second to the highest. Only one more to go. I would like to try it just to see if it would help handling
Any opinions if it would help considering the weight issue I have on the rear? Also what is the best way to raise it? I am sure an automotive hoist would do it. Is it advisable to just trim down the engine, remove the fixed bolts (2) loosen the lower sliding bolts and use the trailer jack to ease it up or am I asking for trouble doing it that way?
posted 05-17-2004 11:18 PM ET (US)
Only, Raising your 150hp seems counter-intuitive since you will loose footing and range of control on tilt and trim. And the additional 100 pounds on the stern of an 18' should not cause such issues. Consider your prop for correct size and pitch. This could be your best fix. Kind regards.
posted 05-18-2004 01:34 PM ET (US)
I don't think that raising the motor will improve handling or porposing. You might try some transom wedges that will increase your down trim angle.
I would experement with your engine mounted higher for top end and less drag. I'd go for the highest possible setting that still gives you a usefull range of trim with out cavitation. I use a "come a long" hand winch and an oak tree. You may have a lifting eye fixed on the engine or need to get one that screws into your flywheel.
posted 05-18-2004 11:27 PM ET (US)
You can easily move your motor just using your trailer, some 2x4's and a floor jack. You can do it right at the landing and it is pretty quick.
There is no fixed formula for what moving your motor up and down does except that it has a significant impact on performance and ride. I can tell you that raising the motor on my Dauntless 15 had a huge impact on reducing porpoising and improving ride, hole shot etc...
I spent a lot of time trying to understand the root causes of porpoising being the engineer that I am. There are tons of opinions of what causes it and how to cure it, but there is very little professional engineering studies that describe it. What they do say is that it is a very complex hydrodynamic system that is influenced by lots of things.
So, lots of people have lots of things that they tried, and they maybe worked very well for their situation and configuration but they really don't know WHY it worked (heck, the marine designers and fluid dynamics guys aren't really sure about it). So, you have to solve these problems experimentally. I'm pretty sure I could cure this through experimentation on almost any boat within reason, but I can tell you that I couldn't tell you why it worked and what the hydrodynamics looked like on a particular configuration.
The usual set of solutions run in order are: engine height adjustment, fin, prop type and selection, trim tabs. You can absolutely solve this problem with tabs, but it is the most expensive (you get a number of other benefits too). You still should make sure, regardless of how you eventually solve this, that your engine is properly positioned vertically.
Just that you added a lot of weight at the back end on the end of a lever arm (kicker and bracket) and it changed the performance of your boat says that you probably need to do some adjusting.
You need to experiment with the boat loaded and driven as you normally would use her. My advice would be to set aside a morning at a launch to do several adjustments and trials.
You can get directions on how to raise the motor without needing lifting eyes or any overhead lift points. It is pretty easy, my wife and I did it several times with our 75HP FICHT, takes about 20 minutes a crack. I can't imagine it is different at all with a larger motor using the trailer method.
look several posts down. I posted a step by step procedure.
You basically strap the boat to the trailer and use the trailer tongue as a big lever arm to move the boat down on the motor. Works great.
posted 05-28-2004 11:05 PM ET (US)
I just raised the motor on my Dauntless 14 foot and I can tell you that it would not have been wise to use the trailer. Some motor mounts may have slotted bottom mounting "holes" but my 2000 75 merc 2-stroke definitely did not. I had to remove all four bolts to raise the motor. Unless it was secured by a lifting eye it wold have been dangerous at best. I also looked over the mounting of new merc's at a local bass pro and they ALL had four sets of five separate mounting holes.
posted 05-29-2004 12:23 AM ET (US)
I just raised the 150HP on the outrage using the trailer. Not a problem. Tilted her all the way down, braced by a couple of 2X4's and strapped to transom using two tiedown straps. Unbolted her, dropped the transom, leaned her slightly and bolted her back on. I did have a friend to help but if I had had to do it myself it would not have been a big issue, the main issue would have been strength. He is a lot stronger than I am which helped getting the bolts started and in getting them tight again. I had 4 separate bolts, no sliders.
posted 05-29-2004 10:05 AM ET (US)
Yes, raising the engine will help stop the porposing, but if you have to much weight in the stern, you still may need to move some forward.
posted 05-29-2004 11:19 AM ET (US)
I am in the process of moving my two batteries foward into the center. I didn't want to give up that storage space, here goes. I have tried all the holes, 4 trips to the lake and it comes down to the fact that a 4 stroke kicker, 2 batteries and a oil tank on the back of an outrage 18 affect the trim of the boat to a degree that can't be adjusted away.
posted 05-29-2004 11:54 AM ET (US)
If moving the weight forward doesn't work, then go to trim tabs.
I am a big fan of them. There are those here who are purists about this and wouldn't use them in any case. However, I have seen them solve lots of problems and add a whole lot of benefit and capability to small boat trim. They will make your boat seem like a much bigger boat in terms of ride since you can position the attitude of the hull to the waves. They will almost certainly remove the porpoising and will give you a ton of trim range back. You might be able to put those batteries back where you had them.
The dynamics of boat trim on a small boat are hugely complex. I don't think it is very easy to predict which adjustment will have what effect for certain. There really is no "intuition" that supports an answer in this sort of thing. The only thing that works is experience with a particular hull or a particular class of hulls. So, if you invest the time in experimentation, you will find a solution.
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