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Author Topic:   Turbo lift--(again)
kshoaps posted 09-14-2003 05:29 PM ET (US)   Profile for kshoaps   Send Email to kshoaps  
I have a sport 150 with the 60 hp four stroke BigFoot motor.

Really love the boat but would like to slow down the minimum planing speed. Right now it planes at 3200 rpm and 16-17 mph (gps).

I am considering a turbo lift from Grand Island Marine.

Does anyone have specific numbers as to performance re: planing, top speed, etc. with and without this device??

Thanks to all


JohnJ80 posted 09-14-2003 08:02 PM ET (US)     Profile for JohnJ80  Send Email to JohnJ80     
I have a turbo lift.

I don't have the specific numbers on before and after, but there was a significant improvement. I am certain that the change is a direct result of the particular boat, motor, load, load distribution and water conditions. So, I am not sure that my experience would be relevant to yours.

On my dauntless 15, with a 75HP FICHT, I can hold plane at about 2700rpm speed is about 14-15mph. I believe your boat and motor combo is lighter than mine so you should have less problem than I do in holding a plane. I am pretty sure that the motor vertical position is going to be important - you may be dragging to much lower unit through the water.

Why do you want to slow down your revs and planing speed? If you are worried about ride in chop etc... then there are other things you can do to. If your motor is too low, this will contribute to a much harsher ride.

Tell us what you are trying to accomplish and we can probably make some suggestions.


kshoaps posted 09-15-2003 08:57 PM ET (US)     Profile for kshoaps  Send Email to kshoaps     
I have no problems with ride quality or control. I simply would like to plane slower without sacrificing much or any top speed.

Members of this board frequently say that the turbo-lift decreases planing speed but never give any numbers.

For those who may be interested: my 150 Sport with 60 hp BigFoot, standard equip. aluminum prop (13 3/4" X 15) clean hull, smooth water and 72 degrees with the engine anti-cav plate at 3/4" above the keel gives the following:

800 rpm-------3.2 mph
1000 rpm-------4.1 mph
2000 rpm-------7.1 mph
3000 rpm-------14.6 mph
3200 rpm-------17.6 mph
3400 rpm-------19.6 mph
4000 rpm-------23.9 mph
5000 rpm-------31.0 mph
5800 rpm-------36.5 mph (engine tilted 8-9 "bumps" to full tilt at WOT)

these are averaged figures using a WAAS GPS.

Note that the boat first planes around 3200 and must be kept at 3200-3400-- to stay on plane. I'd prefer to plane as slowly as possible . How much can the turbo-lift help?


Moe posted 09-15-2003 10:34 PM ET (US)     Profile for Moe  Send Email to Moe     
Just curious, Keith...

Are the speeds at rpms less than 5800 with the trim set all the way in, or with it optimized for fastest speed for that rpm?

What was people/fuel/cargo weight on these runs?

Decided the water intake wasn't too high with the motor raised after all?


kshoaps posted 09-16-2003 02:39 PM ET (US)     Profile for kshoaps  Send Email to kshoaps     
The engine was left at vertical (when floating unloaded) for all the runs except 5000 and WOT. At 5000, tilt up made the engine turn somewhat faster but the boat speed remained the same--also noted a change in the exhaust note so I lowered it until gone (about 5-6 "bumps" from full up tilt).

For wot the engine was again fully tilted up and the exhaust was somewhat louder than normal--I expect some ventilation also occurred. Despite the ventilation with full up, that's where the maxcimum speed occurred. When run vertically, the max rpms are 5500-5600 and speed goes down about 1.5 mph.

For everyday, I leave the motor vertical at about 8-9 "bumps from full up.

Weight in the boat was about 250 lbs of driver, gas and equip.

As to engine height, with it raised 3/4" and trimmed vertical I haven't noticed any problems. I suspect that if I forget the engine in fully up position, the engine note will remind me that the intake is near the surface.

Note that raising the engine increased the rpms by a solid 200.

Moe posted 09-16-2003 05:18 PM ET (US)     Profile for Moe  Send Email to Moe     
Thanks, Keith! I did notice the 200 rpm and 1.5 mph increase this time.


JohnJ80 posted 09-17-2003 08:47 PM ET (US)     Profile for JohnJ80  Send Email to JohnJ80     
Hydro lift decreased my planing speed from 17-19 mph (depending on sea state) to 14-15mph. RMPs decreased from 3200-3300 to 2700 if I am really careful with weight placement and the water is flat.

On my Dauntless 15 with the 75HP, 13.25"x15 prop at a WOT of 5100rpm by max speed by GPS averaged in two runs on recipricol (sp?) courses was 41.5mph with and without the Hydro Lift. This tells me there is very little drag at speed.

What it mostly did for me was the following:
1. Dramatically faster hole shot with far less bow rise.
2. Dramatically improved trim range without porpoising. From virtually none to about 35% in flat water.
3. Much quieter. Don't exactly know why, but I think it has to do with keeping a 'lid' on the exhaust.
4. Much smoother ride, less harsh.

Can you tell us also about the veritcal mounted position on the transom - i.e. which hole the motor is mounted in? Also can you tell us how high your AV plate is above the bottom of the boat?


Moe posted 09-17-2003 10:44 PM ET (US)     Profile for Moe  Send Email to Moe     
Whaler mounts the 60 HP BigFoot on the 150 Sport with the big AV plate right at the bottom of the transom, using the center of five holes spaced 3/4" apart. The water intakes start 1-3/4" below the AV plate.

I don't know about the Dauntless 15, but the 150 Sport stern is flatter (less deep-V in the center) and runs 1" shallower (7" draft) than the 15 Classic (8" draft), so at the transom bottom on a 150, the AV plate is already an inch higher than it would be at the transom bottom on the 15 Classic.

With the motor in the stock location, I've personally never been able to make the boat porpoise, and IIRC, Keith has said the same. In my case, the 13-3/4" X 15" prop ventilates a LOT before max out trim is reached. But then I boat on Lake Erie, where less than 1' of seas is pretty rare.

I also don't have any problem with bow rise on take-off as long as the motor is trimmed all the way in, despite the two of us on the stern seat, and 100 lbs of gas under it, with over 120 lbs of cooler/ice, bait bucket and porta-potti with water in both, behind us. All we really have forward is about 40 lbs of cooler behind the bow locker. I don't think Keith has this problem either. It'll sure rise if you forget and leave the motor trimmed out!

I should probably let him speak for himself, but Keith has raised the motor one hole (3/4"), which puts the AV plate about 3/4" above the transom and the water pickups starting about 1" below the transom. He's reported no ventilation or cooling problems, and picked up 200 rpm and 1.5 mph by doing so. But I believe he boats on flatter water where prop ventilation and sucking air in the water pump is less of a problem.

Just some background.

JohnJ80 posted 09-17-2003 11:47 PM ET (US)     Profile for JohnJ80  Send Email to JohnJ80     
The reason I asked about motor height is that Whaler (per Chuck B) recommends that motors be mounted 0-3/4" AV plate above the bottom of the boat. They will also tell you that this is conservative positioning that seems to work in all conditions.

However, in the same breath they will tell you that you should experiment and set it up properly for your own loads and usage.

What I discovered by going through my repower this year - which turned into a huge science project for me, was that moving the motor up and down (mine started all the way down, about 3/4" below the bottom of the boat) had huge impacts on the ride and performance characteristics of the boat.

My bet is that moving the motor up a bit and trying the planing speed test again might yield different results. You will need less RPM to stay on a plane since you have significantly less drag. You will also be applying your thrust on a vector more along the center of mass of the boat which should be more efficient. You might also be able to use a more favorable trim angle etc.. All of these things might give you much of the same result and would be good to try before spending any money. The ride will probably improve too which might make slower planing speeds less of an issue in rougher water (if that is part of the problem).

If your motor is too low, and you add a fin you might not be solving any problems but creating more due to induced drag. Grand Island Marine recommends that you install this fin and then move the motor UP as high as you can go and still have a cooling stream coming out of the motor. I didn't believe them but then wound up at the same result through experimentation (would have been easier to pay attention and do what they said to do).

So, if the motor is mounted to Whaler's recommendations, I would bet that it is too low. If the boat was repowered and the motor mounted by a non whaler dealer it is almost certainly too low.

The Hydro Lift operates at or above the surface of the solid water at high speed. There you usually don't need a fin since you get enough lift from the AV plate. Then the HL is running out of the water (mostly) and not inducing drag.

I also noticed that it seemed to quiet the motor down, at least the exhaust. I think that it reduced the turbulence of the water around the prop and let it operate in a more 'solid' water environment. So, having this mounted and raising the motor up might also make ventilation less of a problem (qualitative assertion on my part) than raising it up and no fin mounted.

When you are going slower or just coming out the hole, it is providing max lift.

If your motor is too low, you will be dragging the thing through the water and you will have poor performance.


kshoaps posted 09-18-2003 05:33 PM ET (US)     Profile for kshoaps  Send Email to kshoaps     
A simple question--

Why does John's boat go faster with the same propellor turning at a lower rpm than mine does?

Obviously the propellor moving at 5100 rpm should be slower than at 5800 rpm but it is 6 mph FASTER.

Any ideas?

JohnJ80 posted 09-18-2003 08:00 PM ET (US)     Profile for JohnJ80  Send Email to JohnJ80     
It could be several things:

1. My motor is mounted on the top bolt hole where, I believe, your motor is lower in the water. This means more drag so HP is going into pushing more lower unit through the water.

2. My prop is a performance stainless steel, raked and highly cupped Stilletto prop. If you are using an aluminium prop you can be losing speed through more slippage in the water or flexing of the blades. As well, SS props have thinner blades (since SS is stiffer than Al) so there is less drag as the blades slice through the water.

3. Conditions of testing. I tested my speed in flat calm water, early in the morning, freshwater. I worked to get the motor trimmed way up so there was even less in the water (less drag) plus little of the hull in the water (again, less drag).

4. My boat is dry sailed - it sits on a lift (Jet Dock) so there is no growth on the bottom. Bottom is very fair.

5. My motor is brand new, just out of the break in period. This is probably the peak performance on the motor which will degrade slightly over time as it wears.

6. My motor is not a Merc, but an Evinrude FICHT, not to mention 15 more HP (75HP vs 60HP). ;-) (duck, incoming!)

7. My motor could have a different lower unit gear ratio that yours. The Evinrude I have has a 2.03:1 ration. I can't remember whether lower is faster or slower. But if yours is different, then you prop could be turning slower through the water. The RPMs on the tack are how fast the engine is turning, not the prop.

Incidentally, my speed was off of my GPS so we are comparing apples to apples speed-wise.


Moe posted 09-18-2003 09:37 PM ET (US)     Profile for Moe  Send Email to Moe     
At 5800 rpm, Keith's 2.33:1 driven prop is turning 2489 rpm (5800/2.33)

At 5100 rpm, John's 2.03:1 driven prop is turning 2512 rpm (5100/2.03)

John's prop is turning about 1% faster than Keith's prop with John's engine running at 88% of the speed of Keith's engine.

In addition to the prop differences John mentioned, his prop is also a smaller diameter.

But most obviously, John is in an entirely different hull. There are no specs in the continuousWave reference section for the 15 Dauntless, so I can't even begin to compare them.


Moe posted 09-18-2003 09:55 PM ET (US)     Profile for Moe  Send Email to Moe     
To continue...

If Keith had a stainless prop identical to his aluminum (i.e. a Vengence), he might get rpm up to 6,000 rpm at 38 mph or so due to the thinner blades and less flex.

However, if he had the same raked, cupped prop that John does, the additional load it puts on the engine may drop Keiths rpm back to 5600 rpm, and if he was lucky, not drop much below 38 mph.

If he had John's additional 15 hp, Keith might then be able to get back to 6,000 rpm with a speed of 41 mph.

Just some thoughts...

JohnJ80 posted 09-18-2003 11:07 PM ET (US)     Profile for JohnJ80  Send Email to JohnJ80     
Very well said!


kshoaps posted 09-20-2003 02:25 PM ET (US)     Profile for kshoaps  Send Email to kshoaps     
Very interesting discussion, HOWEVER:

The boat obviously cannot go faster than the prop goes.

At my maximum 5800 rpm, the prop is turning 2489 rpm.

IF THERE WERE NO SLIP AT ALL the prop would move forward 15" per revolution or 37680"/min which is 35.4 mph.

Likewise, John's prop at 2512 rpm would move forward at 35.7 mph. IF there was no slip.

The diameter is irrelevant as to top speed (but does figure into acceleration) because his 1/2' diameter smaller prop is still a 15" pitch. Likewise the increased strength and rigidity of SS vs Aluminum props. Flex in my prop will lower my top speed but no lack of flex in John's can ever make it go further than 15" per revolution.

Since 2512 rpm is 2512 rpm regardless if it's attained by 60 hp or 75 hp the engine size is also irrelevant. Hull shape is not a consideration if prop rpm is the same AND we are positing no slip because the boat cannot go faster than the prop.

In fact, working backwards from 41.5 mph REQUIRES that his prop have a 17.4" pitch, not 15".

The testing conditions are the same, flat fresh water, new engine, etc.

REGARDLESS of the boat or conditions, HP, etc. the fact remains that the prop cannot go forward farther than it's pitch and that pitch determines the ultimate top speed for any given prop rpm.

Is John's prop a mislabelled 17"?


kshoaps posted 09-20-2003 02:27 PM ET (US)     Profile for kshoaps  Send Email to kshoaps     
By the way, thanks for the planing speed info I requested.


Moe posted 09-20-2003 07:38 PM ET (US)     Profile for Moe  Send Email to Moe     
Keith, if you consider your rpms, with 36.5 mph, it appears you also have a 17" prop if you're running 9% slip.


JohnJ80 posted 09-20-2003 08:26 PM ET (US)     Profile for JohnJ80  Send Email to JohnJ80     
I think there is more to prop speed calculation that meets the eye. I raised the same point that my speed doesn't match my prop per the calculator. But I am SURE that the speed is right, I have cross checked it several ways on GPS, fishfinder speedo and pitot tube speedo.

When I raised the question several months ago, then others chimed in and said they had noted the same thing.

I have checked and double checked the results, the labelling on the prop etc... I got roughly the same results with my Al prop (somewhat slower).


kshoaps posted 09-21-2003 09:04 AM ET (US)     Profile for kshoaps  Send Email to kshoaps     
Moe-- that's exactly my point--I eliminated slip (totally unrealistic in practice) to make the numbers easier to understand.

If 9% slip is reasonable and indicates my 15" prop is actually a 17" at 36.5 mph, what is the pitch of John's prop (labelled at the same 15") when he's going 41.5 mph?

I believe his prop is mislabeled.


Richard Quinlivan posted 09-21-2003 12:32 PM ET (US)     Profile for Richard Quinlivan  Send Email to Richard Quinlivan     
If you are calculating negative slip obviously the prop has higher effective pitch then labeled.

If the prop is cupped you should add one inch to the advertised pitch. Cupping increases the effective pith at high rpm. Some on-line prop converters include this and some don't. BTW I think all stainless steel and most aluminum props are cupped these days.

Additionally some props have a "progressive pitch", that is the pitch is not constant from the root to the tip. The sdvertised pitch is an average. I beleive that this could yield a different effective pitch then the marked value.

On the Turbo Lift subject I just installed one and have had the boat out twice with it. My boat is a 1995 Dauntless 17 dual console with a 125 Merc two stroke.

The boat comes on plane much better and I can trim much higher before porpoising begins in the 25 to 35 mph range. The boat is much nicer to operate!!

I have not had an opportunity to see what has happened to max speed since the lake was to rough and I had passengers.

BTW the motor is mounted about 1.5 inches up which is thehighest I can get it without a jack plate


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