Question about getting my boat to plane well?

[rdm190]

Let me start off with what I have:

Boat is a 1984 24' Wellcraft Aftcabin. The dry weight of the craft is 4200lbs with a 2400lbs capacity for gear, motor and person. It is powered by a Mercruiser 260 HP chevy based power plant. The outdrive appeares to be a MR or Alpha 1. The outdrive is fited with one of the foils to improve planeing. The prop is a Vortec, 3 blade aluim 15x17 (I assume this is a 17degree pitch on the prop?) The boat has outdrive trim and trim tabs.

I had it out for the first time the other day and it seemed to take a lot of RPM's to keep the boat on plane. I would have to turn at least 3300 RPM's to keep the boat in the mid to high 20's in the MPH (this is where it seemed to plane the best) any less and it seemed to fall on its face and then push the bow way up in the air.

Above 3000RPM's the engine uses a lot of fuel and this just seemes silly to keep the motor spun that high.

Any advice on what I can do to dial this is better would be great. I have a a 15 degree SS prop another 17 degree SS prop sitting around I have not tried. This motor has a 4600RPM redline and running above 3200 rpms is just not fuel efficent for crusing. Will this hull plane somewhere in the teens? or is just as good as it gets

Thanks it advance guys,

Ryan

 

[tashasdaddy]

Re: Question about getting my boat to plane well?

take the foil off the outdrive ( all they are doing is putting umdue stress on the outdrive and the transom, they are trying to pick up the stern of the boat) and just use the trim tabs. the boat is actually under powered to todays boats of that size. you are going to have to bite the bullet and pay the fuel bill or just putt around at idle. i assume you ment that you have adjustable trim tabs mounted on the transom of the boat. if you don't have transom mounted trim tabs, get them.

 

[rdm190]

Re: Question about getting my boat to plane well?

take the foil off the outdrive ( all they are doing is putting umdue stress on the outdrive and the transom, they are trying to pick up the stern of the boat) and just use the trim tabs. the boat is actually under powered to todays boats of that size. you are going to have to bite the bullet and pay the fuel bill or just putt around at idle. i assume you ment that you have adjustable trim tabs mounted on the transom of the boat. if you don't have transom mounted trim tabs, get them.

After reading around on here I did take the fin off. I do have power transom mounted tabs.

I understand that modern 350's are puting out over 300hp, but I really can't believe that 260hp isn't enough to get this boat to cruise well. I am not looking to break speed records, just motor along at a decent pace.

Thanks for your input.

-Ryan

 

[wvit1001]

Re: Question about getting my boat to plane well?

I've got that same engine in a 22' open bow. Mine falls off plane somewhere around 2600 rpm, there's no way it will plane anywhere near 2000 rpm. It gets it's best mileage at around 3200 and trimmed about half way out where it runs at about 35 mph. Trimmed out and at 4600 it runs 55+.

Your boat's a good bit heavier than mine, I don't see anyway your going to get it to stay on plane any much sooner than it is.

 

[cmcpherson]

Re: Question about getting my boat to plane well?

That engine is more that sufficient for that boat, the newer hull designs though are going to allow the plane at lower speeds, but the trim tabs will help greatly in that area. As someone else said, you are probably going to see the best mileage at about 3200 RPM and yes, the gas is going to cost you! Welcome to boating...

 

[QC]

Re: Question about getting my boat to plane well?

Well first off your 260 was rated at the flywheel and the 300 you are comparing it to is rated at the propshaft. You are actually running at about 230 hp compared to modern ratings . . .

Second I think your cruise speed and RPM are actually very good for that combo. A lot of guys cruise in the 4000 RPM range, this is not a car . . . You have to use RPM to make hp, and you need hp to keep that boat on plane.
What we really need to evaluate the performance of all of this is your best WOT RPM. Trimmed properly and loaded as you plan to use her. She should be able to turn between 4200 and 4600 RPM. If so, then it's probably about as good as it's gonna get. You'll find almost all I/O boat combinations get their best fuel economy around 3500 RPM. This is not because the engine is most efficient there, but because the hull is typically just coming onto an efficient plane. If the boat will run above 50 MPH, then this number is closer to 3000, if the boat will only run 35 MPH then this number is usually closer to 4000 RPM.

Also, it is not just the fuel rate you need to consider for economy. It is fuel rate and speed, resulting in MPG . . . Depends if your goal is to get somewhere or spend more time on the lake for less bucks and not really go anywhere. If that's the case try idle . . . That's where she'll get the best overall MPG

Last, are you using your tabs right? Based on your speed numbers, I think you are, but you might do well to review this:

Bennett Op Manual

 

[rdm190]

Re: Question about getting my boat to plane well?

Well first off your 260 was rated at the flywheel and the 300 you are comparing it to is rated at the propshaft. You are actually running at about 230 hp compared to modern ratings . . .

Second I think your cruise speed and RPM are actually very good for that combo. A lot of guys cruise in the 4000 RPM range, this is not a car . . . You have to use RPM to make hp, and you need hp to keep that boat on plane.
What we really need to evaluate the performance of all of this is your best WOT RPM. Trimmed properly and loaded as you plan to use her. She should be able to turn between 4200 and 4600 RPM. If so, then it's probably about as good as it's gonna get. You'll find almost all I/O boat combinations get their best fuel economy around 3500 RPM. This is not because the engine is most efficient there, but because the hull is typically just coming onto an efficient plane. If the boat will run above 50 MPH, then this number is closer to 3000, if the boat will only run 35 MPH then this number is usually closer to 4000 RPM.

Also, it is not just the fuel rate you need to consider for economy. It is fuel rate and speed, resulting in MPG . . . Depends if your goal is to get somewhere or spend more time on the lake for less bucks and not really go anywhere. If that's the case try idle . . . That's where she'll get the best overall MPG

Last, are you using your tabs right? Based on your speed numbers, I think you are, but you might do well to review this:

Bennett Op Manual

Thanks for your very helpfull advice. I took the foil off and am going to do a WOT run tomorrow to see if I can turn 4600RPM's. I got it up to 4000 the other week with quite a bit of throttle left.

Also I am now much more educated on how to use my trim tabs, I have a feeling I was useing them pretty poorly, as well as my drive trim.

On a side note, is there any advantage to using an alunimum prop over a stainless one? I have both with the same pitch.

-Ryan

 

[QC]

Re: Question about getting my boat to plane well?

On a side note, is there any advantage to using an alunimum prop over a stainless one? I have both with the same pitch.

Yeah, they're cheaper . . . Use the stainless. Well first, use the one that gets you in that 4200 - 4600 window. Many here will disagree with me, but if she'll pane, and you want economy more than liveliness, you want to be closer to the bottom of that range if your load is typical. Lighter than usual? Go towards the top.

If you have two props, one stainless and one aluminum, theoretically the stainless will be more efficient, less "slip" which is a prop efficiency measure. There are bad Stainless props though and good aluminums, and this can vary from boat to boat. Spend a little time reading on the prop forum vvvvvvv that might help. BTW, the one towards the bottom of the range may actually be faster top speed too, some of this is counter-intuitive for sure . . .

 

[rdm190]

Re: Question about getting my boat to plane well?

Thanks for all your help guys,

Today I got her out with the following results:

The weather was less the good, windy and a bit choppy about 69 degrees 70 degree water.

I removed the silly hydrofoil. I trimed the prop to the bottom and the tabs all the way down. I nailed it and it got up on plane super fast. I backed off on the tabs and prop trim to get a nice even angle. The result was about 40mph @ 4600rpm (my motor's redline)

I then played with it for about 30 min and got it to cruise at about 25mph @ 3200rpm. This resulted in exactly 10gallons per hour fuel use. This seems like some good economy (opinions welcome on that point).

I still had the aluminum prop on today, but I just switched out to the stainless prop of the same pitch. We will see if I get a better hole shot on saturday with the less flexible stainless prop.

Anyway I was very happy with the performance of my now 23 year old boat.

I only had three people (including me) on the boat today, what should I do to maintain this performance with additional persons onboard?

-Ryan

 

[QC]

Re: Question about getting my boat to plane well?

I removed the silly hydrofoil.

Awesome!

I trimed the prop to the bottom and the tabs all the way down. I nailed it and it got up on plane super fast. I backed off on the tabs and prop trim to get a nice even angle.

Perfect!

The result was about 40mph @ 4600rpm (my motor's redline)

It sounds like you backed off and if so, you may need more pitch to slow it down a little. The range of 4200 - 4600 is not redline as you know it. It is where she should fall at Wide Open Throttle, sustained. Some guys run so that they can exceed the max WOT RPM for better hole shot, but economy and top speed will suffer. If you don't need the hole shot and it can exceed 4600, you should go up in pitch slightly. 2" may be a lot, but if economy is the goal, and she planes easily now . . .

I then played with it for about 30 min and got it to cruise at about 25mph @ 3200rpm. This resulted in exactly 10gallons per hour fuel use. This seems like some good economy (opinions welcome on that point).

OK . . . 3 MPG would be great, but an aft cabin model is probably heavy enough to force it down to 2.5

less flexible stainless prop.

Usually the flexible Aluminum has the better hole shot (flex is like lowering pitch) and the Stainless has the best top speed because it doesn't flex . . .
With higher weight, it will perform worse in every performance category. If you had hit 4600 at WOT (trimmed right, max, flat out) I would say leave it alone if you expect higher loads.

 

[rdm190]

Re: Question about getting my boat to plane well?

So you think the SS prop will be a bad choice? I will give it a shot, only takes 5min to switch.

Also, your saying I could add another degree or two to my prop pitch? Maybe a 18-19 degree prop? Or did I missunderstand you?

-Ryan

 

[Scout Sport Fish]

Re: Question about getting my boat to plane well?

260 does sound a little low. Does it still have a Capacity Plate somewhere? They state what the Recomended HP (which I see as the minimum) and max HP can be on the boat. My min is 115 and max is 150. My boat is a 185 Scout with an 8 foot been and a nice fairly deep V hull.

 

[athiker]

Re: Question about getting my boat to plane well?

Adding to QC's comments re: flex. If you can over rev now the SS may be perfect. You may not get quite the holeshot b/c your engine may take a bit longer to get its revs up w/ the firmer/stiffer blades holding the 17p shape, but by the same token at WOT the SS blades won't be flexing flatter under load like the aluminum may be so it may lower your rpms a bit and give you a higher WOT speed. Under load your alum may flex to something less than the full 17p shape it has under no load.

Of course the wild card in this is if the alum and SS props have the same pitch but vastly different rakes, cupping or other characteristics that could affect relative perfomance.

 

[rdm190]

Re: Question about getting my boat to plane well?

260 does sound a little low. Does it still have a Capacity Plate somewhere? They state what the Recomended HP (which I see as the minimum) and max HP can be on the boat. My min is 115 and max is 150. My boat is a 185 Scout with an 8 foot been and a nice fairly deep V hull.

The boat came with 260 from the factory. No HP ratings on the capacity plate. Wellcraft offered this boat with 3 motors, the 260 being the highest HP rating at that time.

I know you guys are all compaing it to newer boats with globs more HP but 260 is MORE then enough to get this boat moving. It did 40 in choppy water with no tuning and a novice behide the helm. I would bet it will see 45 on a nice day and I get my prop dialed in right. Some of you may be speedsters, but I have a seadoo that will do 75mph all day long, so it cures all my speed itches.

Thank you all for your comments on the HP rating, but 260 is what this motor came with in 1984 and short of the block gernading that is how it is gona stay. At this point I am trying to get the BEST possible speed/performance/economy out of my setup. This is just a nice crusier to take some friends up and down the river and do some fishing. I would love to own a newer high HP boat, but I just can't afford it.

Thank you again everyone for your input. I will see how it does with the SS prop on Saturday. Any further advice is more then welcome.

-Ryan

 

[QC]

Re: Question about getting my boat to plane well?

If you can over rev now the SS may be perfect.

Yeah, I agree with athiker's comments. Still not sure if you are capable of exceeding the 4600 RPM with the Aluminum . . .

 

[rdm190]

Re: Question about getting my boat to plane well?

Yeah, I agree with athiker's comments. Still not sure if you are capable of exceeding the 4600 RPM with the Aluminum . . .

I don't think it will exceed 4600 with the aluminum prop, I had it flat out today and it held at 4500-4600. Pehaps as I get better with the tabs and propr trim I could have squeezed another 100 out of it.

Like you guys have all said I will try the SS 17p SS prop. I also have a 15p SS prop, is there any point to giving that a shot? or is that a move in the wrong direction?

 

[studlymandingo]

Re: Question about getting my boat to plane well?

You are probably going to be propped correctly with the 17P SS; the 15P will give you better hole-shot, but you're going to be pegging the RPMs hard. I would probably take it with me and give it a try just to see. May give positive results.​

 

[rdm190]

Re: Question about getting my boat to plane well?

Thanks again for all the responses guys and galls. you all have a great forum here.

I am going to throw another question out there. When I had the boat out testing I had three normal sized adults on it. I had no issues with the boats forward atitude. However my craft has a large rear seat (basicly on the transom) that can seat 4 adults with no problem whatsoever. I think this type of load is going to send my bow skyward. If I am unable to trim this type of situation out smoothly with the tabs would adding some ballast in the bow help? I have a ton of bow storage and was thinking of some sand bags.

I figure on a good day I could possibly have 4-6 adults and a few small children on the boat. I would still like to be able to get where I need to go without having to idle there! I know having 500lbs of extra person over the transon is going to have a large impact, but will my tabs be enough to keep the stern out of the water?

-Ryan

 

[studlymandingo]

Re: Question about getting my boat to plane well?

Man, don't take any sandbags with you!!! You can probably adjust the boat's attitude pretty well with the tabs; you may notice the boat being slower to plane with the weight at the stern though. If you want to shift some weight, move the batteries forward, but don't carry any more weight than you have to.​

 

[rdm190]

Re: Question about getting my boat to plane well?

Man, don't take any sandbags with you!!! You can probably adjust the boat's attitude pretty well with the tabs; you may notice the boat being slower to plane with the weight at the stern though. If you want to shift some weight, move the batteries forward, but don't carry any more weight than you have to.​

I figured adding weight would be counterproductive

I know it is going to be slower and react differently with more people on it. I just hope I can enjoy it as much with a buncha friends!