Redistributing weight after repowering

[Bgbbgb246]

I recently re-powered my 19-ft Fisher shallow v bass boat with its maximum horsepower of 150 horsepower. On the first test drive I quickly realized that I would have to remove my 10" jack plate as the boat sat very unlevel. (I know the ridiculously big Jack plate to try to use on the maximum horsepower engine. I wasn't really thinking) After removing the jack plate and mounting the engine straight to the boat The boat sat pretty much th same way in the water as it did with the 115 horsepower with a jack plate. The only noticeal difference now is that at speeds after putting speed and before plane, the bow of the boat comes up in the air quite a bit further than it used to and remains there until on plane. It's not really something I can't live with but it cuts out a bit of my visibility and sometimes you just have to travel at that slow speed in channels and shallow areas. I understand this may end up just being a give and take where I get the top speed that I want but with a few trade-offs. I cirtainly prefer the extra 12 mph. However, I was thinking of some possible solutions to my issue and one of my thoughts was reducing the weight in the rear end of the boat. It has a 39 gallon tank that probably weighs about 230 lb full. Obviously I can't really move that and also it's designed intelegently to to put a lot of the fuel behind the bench seat instead of by the transom. But what I can move is the three large 12 volt batteries that sit right against the transom; 2 on one side and one on the other. I have a compartment that I never use it's about 3 ft behind from the very front of a boat. It's big enough to fit all three batteries. now I figure these three batteries probably way a combine total of 120 to 150 lb and I think moving them this far forward may help even out the distribution of weight in the boat and make up for the added weight of the bigger engine. The wiring from the trolling motors should be pretty easy routing as the trolling motor is just right there. Running the leads from the motor to the front of the boat will be a little bit of a job but something I'm willing to do. what do you guys think? Do you think this amount of weight all the way at the front of the boat will even the boat back out, or do you think it's not worth the effort.

 

[Old Ironmaker]

My StarCraft Superfisherman 190 sat too high for me when at slow speeds as well after I added a 15HP kicker on the transom. Not good vision. I removed the 12 volt batteries in the bow because I didn't need them as I removed the elec. troller. I put the batteries back in for ballast and it helped a lot. Those batteries were heavy I would say at least 70lbs each. I moved my anchor ahead in the bow and that helped. Weight distribution is important to get the bow down before planning speed.

 

[dingbat]

You shouldn’t need to move weight around with a maxed out transom. The boat should rocket up up on plane.

You need a prop with more lift. What prop are you running?

 

[ahicks]

You shouldn’t need to move weight around with a maxed out transom. The boat should rocket up up on plane.

You need a prop with more lift. What prop are you running?

Sorry, I'm going to disagree a little bit. Granted, you don't HAVE to shift weight, but I think the question here is is it a good idea? To that, I believe the answer is a great big yes. There is no upside to dragging that weight around in the rear. None. If that weight needs to be onboard, there's no reason it can't be installed in a place that will improve the safety and handling of the boat.

This is no different than moving the kids up front when pulling a skier with a bow rider. It just plain works better.

Not going to disagree with the 4 bladed prop, unless top end really is a priority. Those aren't going to hep a bit in that department.

When moving the starting battery forward, don't forget you'll need to increase the wire size significantly or suffer greatly reduced cranking speed/starter performance.

 

[QBhoy]

Is this a boat rated at 150hp 2 stroke or 4 stroke ? Which do you have now ?

 

[QBhoy]

Referring to my above comment...all but the very most recent 4 strokes are way heavier than the older 2 strokes.
Apart from that...is the prop well suited ? I’ve never needed it on any of my boats...but smart tabs might have a use here ?

 

[Chris1956]

Adding HP should make the boat come up on plane with LESS bow rise. Make sure the motor can trim down tight to the transom. Also, the Jack Plate should never take away performance or cause list, as you have described.

The Jack Plate may not add performance, and it does shift the weigh to the rear somewhat, causing the boat to sit lower in the water. However, it should not cost performance.

A 19 footer should handle a 150HP motor easily.

In conclusion, something about your setup is incorrect. Not enough trim in, too tall a pitch on the prop, motor mounted incorrectly....

 

[Bgbbgb246]

Im going to try to adress this all to keep things informative.

You shouldn’t need to move weight around with a maxed out transom. The boat should rocket up up on plane.

You need a prop with more lift. What prop are you running?

Boat has no issue getting on plane. Fantastic holeshot and about 53mph top speed. The bow simply comes up to a slightly irritating level when im forced to go say 15mph for example.

This is no different than moving the kids up front when pulling a skier with a bow rider. It just plain works better.

This was my exact theory.

Is this a boat rated at 150hp 2 stroke or 4 stroke ? Which do you have now ?

Its a 2stroke.1997 merc xr6 that replaced a 1995 force 120

Adding HP should make the boat come up on plane with LESS bow rise. Make sure the motor can trim down tight to the transom. Also, the Jack Plate should never take away performance or cause list, as you have described.

The Jack Plate may not add performance, and it does shift the weigh to the rear somewhat, causing the boat to sit lower in the water. However, it should not cost performance.

A 19 footer should handle a 150HP motor easily.

In conclusion, something about your setup is incorrect. Not enough trim in, too tall a pitch on the prop, motor mounted incorrectly....

I dont think you quite understand my issue. I probably did a poor job of explaining. As i said above "Boat has no issue getting on plane. Fantastic holeshot and about 53mph top speed. The bow simply comes up to a slightly irritating level when im forced to go say 15mph for example."
With the jack plate the boat went even faster than it does now. However, as you said, this shifted the weight backwards and with the new heavier engine this caused the boat to be too rear heavy for me to feel comfortable with it. removing the jack plate fixed this.

My StarCraft Superfisherman 190 sat too high for me when at slow speeds as well after I added a 15HP kicker on the transom. Not good vision. I removed the 12 volt batteries in the bow because I didn't need them as I removed the elec. troller. I put the batteries back in for ballast and it helped a lot. Those batteries were heavy I would say at least 70lbs each. I moved my anchor ahead in the bow and that helped. Weight distribution is important to get the bow down before planning speed.

Seeing this, i think ill give it a shot. Your situation seems very similar to mine. I dont know that ill be able to completely get rid of the bow rise at slow speeds but any improvement would help make me happly. Like i said, Im not super concerned with this new behavior at slow speeds as its not that often that one would have to travel at that speed. But, better weight distribution would make it a little more user friendly.

Ill check in with everyone after i test it out to let you know the results.

thank you all

 

[dingbat]

Boat has no issue getting on plane. Fantastic holeshot and about 53mph top speed. The bow simply comes up to a slightly irritating level when im forced to go say 15mph for example.

Your bow comes up because your not generating enough lift at the transom.

To resolve, you can either generate more lift on the transom or move weight forward which may or may not affect your ability to raise the bow should the need arise.

You didn't mention what prop your running. In this situation a prop can be an asset or a liability.

A set of tabs, either fixed or adjustable, would make the problem go away altogether

 

[Bgbbgb246]

Your bow comes up because your not generating enough lift at the transom.

To resolve, you can either generate more lift on the transom or move weight forward which may or may not affect your ability to raise the bow should the need arise.

You didn't mention what prop your running. In this situation a prop can be an asset or a liability.

A set of tabs, either fixed or adjustable, would make the problem go away altogether

I run a 21p SS Apollo XS with maybe 5 hours on it. The motor runs at max rpm with me, a buddy, and gear. Could probably be propped up a pitch or two just judging by the tach, but props are expensive and i just avoid running her full throttle when I can. I guess i just dont understand what you mean by a prop generating "lift" on the transom. The way i see it is that the only thing that will produce "lift is the angle of the outboard (it is all the way down) and possibly a big-ol anti-cavitation plate. I dont really see how a different prop would effect either of these.

My only other idea is that i suppose i could move the engine up a little bringing the prop closer to the boat thus causing less torque. However i don't really think i can bring it up more than maybe a bolt hole or two without causing a ventilation issue.

Also i suppose that tabs would work but not really something i plan on doing for something thats really not that big of a deal

 

[ahicks]

Prop lift is a pretty advanced concept, usually involved when going for that last couple of percent of available performance, so not many will concern themselves with it. A good example though, would be the extra "lift" generated by a 4 blade prop. Many people that have tried them or are running them will comment that the boat stays on plane at lower speeds than it used to - which is due to 4 blade "prop lift".

A 4 blade might help your issue, but my guess is the 4 blade could cost you a couple miles an hour too.

As far as height on transom, if you are able to change it yourself safely, I do believe that's worth setting correctly. There is NO advantage to running a motor any deeper than necessary.

 

[Chris1956]

Running below planing speed on any planing hull will cause the bow to rise. It is the nature of the beast. How high the bow rises is dependent on the hull style, the exact speed, the power of the motor and other factors.

Quickest plane and lowest bow rise will be achieved by full throttle off idle speed.

Moving the engine up a mounting hole, does not cause less torque. It can cause less trim effect, however.

I would recommend you run the boat at planing speed and observe the anti-ventilation plate. It should be above the water line, if the motor is at the correct mounting height.

In addition, on that boat, the A-V plate could be 1/2 to 1 inch above the water surface, and it could give superior performance..

 

[dingbat]

I guess i just dont understand what you mean by a prop generating "lift" on the transom. The way i see it is that the only thing that will produce "lift is the angle of the outboard (it is all the way down) and possibly a big-ol anti-cavitation plate. I dont really see how a different prop would effect either of these.

http://continuouswave.com/whaler/reference/prop3.html

Every hull behaves differently. I see everyone jumping on the 4 blade band wagon, yet I swapped out a 4 blade for a 3 blade of an entirely different prop design and was blown away by the results. Ended up with a better hole shoot and a faster top end but gave up 100-150 rpm in the mid-range which I could care less about.

Scratching my head over the "stay on plane longer" claims since planing speed is a function of hull design. Guessing the additional lift they provide at lower speeds gives the perception of staying on plane at lower speeds.