Does raising the motor up higher on the transom help the boat plain better.

[themoodystwo]

I see that my boat motor is on the lowest settings on the mounted bracket that it is on. It only is a 55 hp yamaha and someone told me to raise it up higher on the mounted brackets so it will sit higher in the water and help with take off.. Will that help it any with the plaining. Thanks

 

[kfa4303]

Re: Does raising the motor up higher on the transom help the boat plain better.

motor height can have a huge impact on performance. the anti-vent plate, found just above the prop, should be level or 1"-2" above the keel. You'll also want to adjust the trim/tilt to dial in the best results. mostly just takes lots of trial and error.

 

[Bob_VT]

Re: Does raising the motor up higher on the transom help the boat plain better.

There are two adjustments........ one for the height of the motor and one for the trim angle of the motor. The lowest trim angle .......which is against the transom and kind of "tucked in" which will help a boat plane the fastest.

Post a photo of the current set-up.... what exactly is the problem? Planing the hull? Top Speed?

 

[Philster]

Re: Does raising the motor up higher on the transom help the boat plain better.

The shape of the hull matters.

Lacking that info it is hard to answer.

Flatter-bottom = higher up.

Deep V = lower down

Setback matters, too. If the engine sits on a bracket farther back, the engine should be raised even more. Generally, 1" for every 8-10" of setback.


The prop really needs something to bite into to make a deep V rise. On a flatter bottom, which includes bass boats and Skiffs, the prop is not doing very much lifting, since the hull is basically going to sit on top of the water as soon as it starts moving. So, the prop can be higher.

So.... it depends. AV plate even w/ bottom is a good, blind starting point.

 

[Texasmark]

Re: Does raising the motor up higher on the transom help the boat plain better.

All good info, but I do something else sometimes. I have a large engine on a light fast boat. Transom has 3 flat steps to it, each about 1" from the other, no V. Avitar is the wake at 50 mph.

My engine is jacked up one 3/4" notch and I have a high pitched Ballistic XL SS prop. Sometimes I will deliberately be trimmed out, maybe 10 degrees from vertical when I hammer down on it in the hole. The engine will start chugging and somewhere along the process, we're talking about a 3-5 second plane out, the prop breaks loose and the rpm's shoot up maybe 1000 for a guess. When the prop locks back up, the engine is now well up on the hp curve. It bites again with a lot more whoopie driving it and the boat shoots forward but breaks loose again, ditto, ditto, and in no time flat I am blasting across the lake.

But seriously, for normal hole shots the others have it covered.

On raising the engine, I had a 15' FG Kingfisher bass boat once with a flat transom area, actually flat most of the bottom with a hint of a V at the bow, with a 70 hp rude. I had a SS prop and got what I thought was pretty good performance. Had no speedometer or tach (primitive years back then) so I just know how it sounded and felt. One day I jacked it up one notch and put a 1x2 piece of redwood between the engine and transom top and bolted her back down. The result of that little measure was stellar. Really made a difference. No brag, just fact.

Mark

 

[themoodystwo]

Re: Does raising the motor up higher on the transom help the boat plain better.

I am a first time boat owner and this is the one I bought. I only paid $2,800 dollars for it. I didnt want to buy anything bigger until I made sure this is what I want to spend money on for enjoyment.. I will get some pictures of the back for you guys to take a look at. Thank you for your post's.

 

[themoodystwo]

Re: Does raising the motor up higher on the transom help the boat plain better.

Here is a picture of it Bob_VT I will post more for you.My problem is plaining out. Thanks

 

[Philster]

Re: Does raising the motor up higher on the transom help the boat plain better.

Winner winner chicken dinner.

Generally, the prop centerline on a boat like that can be as close as 3-4" below the bottom and the AV plate upwards of 5" above or more.

No need to bury the prop on a rig like that.

Where does the prop centerline or AV plate sit now?

To get on plane, be trimmed down. Once on plane, trim it out and RPMs rise w/out adding more throttle and stop trimming.

 

[themoodystwo]

Re: Does raising the motor up higher on the transom help the boat plain better.


I took pictures of the back of the boat.One picture is the motor all the way down the second is the transom and bracket to see if moving it up would be a good idea and the third is my prop, it is a 13 3/8-G. The issue im having is my boat will not plain with 2 people sitting in the back one of us has to move to the front in order for it to plain out.

 

[jimmbo]

Re: Does raising the motor up higher on the transom help the boat plain better.

Picture from the side with engine vertical taken with the camera even with the bottem to, no angle up or down, would be better. Also positioning a straight edge down the keel and extending out the back would also make it easier to see what we are looking at.
Raising the engine is not normally done until a boat is capable of going over 50mph. unless someone put a 20 inch engine on 15 inch transom. Up to 50mph the anti ventilation plate is usually postioned flush with keel when it is trimmed pararell to it. Raised engines also have less ability to lift the bow at high speed due to lower leverage. Finally to run at higher transom heights the ole stock aluminium prop just isn't gonna cut the mustard

 

[themoodystwo]

Re: Does raising the motor up higher on the transom help the boat plain better.

Picture from the side with engine vertical taken with the camera even with the bottem to, no angle up or down, would be better. Also positioning a straight edge down the keel and extending out the back would also make it easier to see what we are looking at.
Raising the engine is not normally done until a boat is capable of going over 50mph. unless someone put a 20 inch engine on 15 inch transom. Up to 50mph the anti ventilation plate is usually postioned flush with keel when it is trimmed pararell to it. Raised engines also have less ability to lift the bow at high speed due to lower leverage. Finally to run at higher transom heights the ole stock aluminium prop just isn't gonna cut the mustard

Thank you for your information. I will get more pictures posted soon.

 

[Philster]

Re: Does raising the motor up higher on the transom help the boat plain better.

Looks low, but need better pics for sure.

 

[Bob_VT]

Re: Does raising the motor up higher on the transom help the boat plain better.

Here is the best suggested view for the motor/transom Use a straight edge

 

[Texasmark]

Re: Does raising the motor up higher on the transom help the boat plain better.

Here is the best suggested view for the motor/transom Use a straight edge

My personal preference would be to move about 2' forward around the side of the boat, get down where you can see clear across the bottom, put a straight edge, one long enough to lie flat with the bottom of the boat and touching it the whole length (parallel), then extend to the engine and move the tilt until the AV plate is parallel with the straight edge. Then we can see where you are. In this picture it appears that the engine is tilted out and the straight edge is not parallel with the hull. May be, just looks that way. Moving the camera around the side as I mentioned would help me to get more out of this pic. Sorry, personal opinion.

Mark

 

[Philster]

Re: Does raising the motor up higher on the transom help the boat plain better.

Yeah, boat and motor need to be 'flat' in relation to each other, which usually means not quite trimmed down/in all the way, so that the AV plate (above prop) lines up level with the boat, for lack of a better description. Yours looks like it could be trimmed in some more for the pic.

 

[Texasmark]

Re: Does raising the motor up higher on the transom help the boat plain better.

By the marking on the side, appears to be an older trihull at 15 1/2 ft. Is that a 90 hp Yammie?

Back in the day, I saw lots of them with 85 rudes swinging OMC SS props. Seemed to be a good combo and didn't seem to have hole shot problems.

I have a 90 Merc and once compared cubes with the 90 Yammie and found them to be light for the hp. I was thinking of upgrading my rig to 115 hp (rated for 130) and was viewing a Yammie catalog.

When you are trying to get a "pad" boat like yours on plane with 2 people aft of center, usually 3 batteries right in front of the transom on one side with 20 or so gal of fuel on the other, and a 20 gallon live well between the passengers and the other stuff, you have a real load on the engine.
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When Merc came out with their V6 150 hp engine which certainly was intended for the BB market, it was a 2 liter, my son had one. Wasn't too long after that they came out with a redesign and a new fancy name but basically it was the same 150 HP rated engine but now it had a 2.5 liter block. Well it doesn't take a rocket scientist to realize that "size matters" in stock car racing, dragsters, and BB's......big blocks, more cubes.

I'm going to say that to get where you want to be with that rig, you get a ported SS high performance bowlifting prop like the one in Bob_VT's picture of the proper pitch.....after we figure out your current height and work that.

What the ports will do is allow the engine to rev in the hole shot getting it's rpm's developed so that the engine doesn't lug (2 strokes hate to lug) and get you "outta da hole". Ported props were designed for the BB community for just that purpose. I have one which I ported myself and got the desired results.
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I just finished working with a guy that had a hole shot problem with an OMC Sea Drive on a deep V fishing boat. He actually had to tilt his engine almost out of the water to get it ventilating then trim down to even get on plane. The forum was boating and the thread was "engine height" or something like that......engine something in lower case letters. I'll go find it and edit this post so that you can see first hand what I am talking about.

We got his ports out to 3/8" and solved (to his satisfaction) what was looking like a very complicated engine height problem....the Sea Drive installation didn't lend itself to jack plates and all.

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edit: It's in the Boat topics, first forum in the forum list, today it is on Page 3 and the title is "motor position". Take the time to walk through the entire thread. Then see if it applies to you.

My 2c,
Mark

 

[themoodystwo]

Re: Does raising the motor up higher on the transom help the boat plain better.

One picture is just a measurement from the bottom of the boat motor to the bottom of the boat anothe picture is a stick that is level and coming straight out with the motor all the way down and the other picture is the stick coming out with the power tilt and trim moved up a bit to where it is level with the bottom of the boat

 

[themoodystwo]

Re: Does raising the motor up higher on the transom help the boat plain better.

There is room on my motor brackets to raise the motor up about 2 inches. Will this help me plain out better on my boat. What is happening is when 2 of us are in the boat and want to take off if we both sit in the back the motor just seems to run low until I move up closer to the front and then the rpms start raising and the boat picks up speed and then it will plain out. Ive tried the tilt and trim but that isnt working. my prop is a 10 3/8 x 13-G. If I need another prop to plain out can you guys tell me what I need or can I just raise the motor up and see what that will do. Thanks

 

[kfa4303]

Re: Does raising the motor up higher on the transom help the boat plain better.

Hi themoodystwo. I clamped my motor ('66 20 hp) a few inches higher on the transom as you described and it did improve the overall performance. Of course, eventually you run out of transom. The problem for most folks with vintage OMC motors seems to be that motors of that era had sort of an odd 18" leg length which put right between modern short and long shaft motor which are generally 15" and 20" respectively. As a result, lots of guys have to raise the motor a few inches just to get the anti-vent plate to be level with the keel as it should be then several more inches to notice much of an improvement. While there are certainly all kinds of infinitely adjustable jackplates that you can buy, or make yourself here's an interesting "transom raiser" of sorts that I stumbled across recently. It basically just gives you more clamping height for your motor, but as you can see it's super simple, easy to do as a DIY project and appears to be quite strong and suitable for motors under 35 hp, or so.

 

[jimmbo]

Re: Does raising the motor up higher on the transom help the boat plain better.

Hi themoodystwo. Looking at the pics you posted I would say your engine is mounted at about the best height for your setup. That takes into account your boat, the hp of your engine, your propeller. and the probable speed you will attain with that combo. Raising the engine ny higher and you face the very real possibility of ventilation. It will be a chore to operate the boat rather than enjoyment. You won't be able to trim as far out as before, in turns the lose of bite will be ongoing, even accellerating could be a chore. Going to a performance Stainless Steel prop will help a bit. Even at higher speeds like in the mid 50s each inch raised is only worth about 1 mph. You are free of course to do whatever you want