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Author Topic:   90 on a 15' sport
gtcway posted 06-08-2004 10:51 PM ET (US)   Profile for gtcway   Send Email to gtcway  
Anyone have a 90 hp engine on a 15' sport or tried it? I'm curious what the top speed is to compare it to my boat.
where2 posted 06-09-2004 12:46 PM ET (US)     Profile for where2  Send Email to where2     
Mid 50's...with the right prop. Not drastically faster than with a 70Hp... As you approach 50MPH with the 15' hull, it becomes generally unstable feeling due to chine walk on the rounded keel in the last few feet of the hull in front of the engine. Unless you're psychotic, surpassing 45mph with this hull is only possible on glassy calm water with no chance of wind gusts.

My comments are not based on having run a 90HP, but simply on the effects of approaching 50MPH with the 70Hp engine turning a 19" SS prop with extra cupping. The 70hp will do an even 50mph with the right combination of gearing and prop.

Peter posted 06-09-2004 02:26 PM ET (US)     Profile for Peter  Send Email to Peter     
I have a 15 Super Sport (bottom painted) with a 70 mounted all the way down on the transom turning a 19P aluminum prop. It will go 42 to 43 MPH tops (GPS measured, multiple directions) at 6000 RPM. This speed is within 1 MPH of the predicted top speed for the 15 hull. To get 50 MPH out of a 15 with a 70, the motor would have to be raised up significantly to the point that it might not be controllable.

Due to the rounded stern shape, the 15 hull starts to chine walk at speeds over about 38 MPH. It can become quite a handful at 42 to 43 MPH. I can't imagine wanting to go much faster than that in the 15, but with a small 90 HP, predicted top speed is about 48 MPH. I think that mid 50s is not likely without significant engine lift which would probably lead to a severe loss of control.

gtcway posted 06-09-2004 06:38 PM ET (US)     Profile for gtcway  Send Email to gtcway     
I have a 1999 Evinrude Ficht 90 on my 15' whaler. When I first put it on it was uncontrollabe at WOT. I was working as a mechanic at an OMC dealer in the Bahamas at the time and one of the other mechanics helped me design a jack plate out of aluminum I-beam. I'm running a 20P Raker prop and I get around 6300rpm tilted out and it's surprisingly stable. When I put it on I was getting 57mph, checked with a gps. Since then I've painted the bottom and I can only get 53-54mph, still at 6200rpm. I considered having the pitch increase to 22. Does anyone have any experience with changing the pitch? I don't want to do it if it might ruin the prop.
Flipper posted 06-13-2004 11:29 PM ET (US)     Profile for Flipper  Send Email to Flipper     
With a '99 90 Merc on a jackplate and hydraulic steering, I am getting 56mph at 5200 rpm with a 26' pitch Laser2. (pic. on page 50)I know I can get 60 with more rpm's, higher jackplate settings and a different prop, but I need a boat that is still useable and practical!
My boat actually goes the fastest when there is a 6"(or so) chop, when the hull is even more "unstuck". The hydraulic steering makes all of the handling a dream. There's no more fighting with steering torque or chine-walk.
Bigshot posted 06-15-2004 11:24 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
I have been on one with a 115 Ocean runner but we could NEVER get it WOT, too damn unstable.
gtcway posted 06-15-2004 12:35 PM ET (US)     Profile for gtcway  Send Email to gtcway     
I do have hydraulic steering. Next time I have it in the water I'll have someone take a picture while passing at WOT. I've been told that only about a foot of the boat is left in the water.
montauk madness posted 06-15-2004 01:36 PM ET (US)     Profile for montauk madness  Send Email to montauk madness     
My last whaler was a 15' with a 1989 90hp Mercury engine. It went 50 mph +/-. The engine was mounted one hole up. I don't know what pitch the prop was.

I didn't have much problem with porposing etc. However, it was manual tilt and that got old.


BOB KEMMLER JR posted 06-15-2004 04:09 PM ET (US)     Profile for BOB KEMMLER JR    
Do you think the Mischief models would handle a bit better due to the extra weight from the hull cap?I'm thinking of getting one of these in the near futre and would definately overpower it.
Buckda posted 06-15-2004 04:50 PM ET (US)     Profile for Buckda  Send Email to Buckda     
Here's my 15 Sport at full throttle with one adult and young teen aboard in the North Channel last summer. You can see that there is not much hull in the water at all.

At about 28 MPH and in about an 8 inch to 1 foot chop, it can be planed down to a more stable ride:

I would definitely recommend hydraulic steering if you're going to the 90, as the 70 already has quite a bit of resistance at speed.


where2 posted 06-17-2004 01:06 PM ET (US)     Profile for where2  Send Email to where2     
Having recently upgraded to Baystar Hydraulic steering on my 15'(Sport not SS). I can assure you anything else I ever buy will get a Baystar or a SeaStar if it doesn't come with hydraulic steering...

NOTES: Having no bottom paint really helps the speeds. Mine never had paint, and never will... Having a driver that weighs 135lbs has to help... Using an SS prop improves top speeds...

Flipper posted 06-19-2004 06:08 PM ET (US)     Profile for Flipper  Send Email to Flipper     

Nice rig. I'll post some shots soon.

gtcway posted 06-19-2004 09:51 PM ET (US)     Profile for gtcway  Send Email to gtcway     
I have some picture posted here:

where2 posted 06-20-2004 12:31 AM ET (US)     Profile for where2  Send Email to where2     
GTCWAY: If that's a stainless prop on your rig, then Stainless is definitely capable of being repitched once. Unfortunately, finding a shop to do it may take you all over the islands... The alternative is to find a different prop in the pitch you want, which gets expensive in the islands.

I let the local prop gurus in West Palm Beach, FL beat the cupping back into my 19P SS prop, then I started drilling vent holes behind the blades as yours has... The vent holes were to see if I can come up with a way to pull up a slalom skier with my 19P prop...

gtcway posted 06-20-2004 12:19 PM ET (US)     Profile for gtcway  Send Email to gtcway     
Yes it is a stainless prop, an OMC Raker prop. I bought it used from a friend. It holds much better than the standard OMC stainless props with the engine running so high. With it, I can trim the engine to the maximum trim angle and not lose it's grip. It used to be shiny but the local prop shop sanded it and painted it black when I took it in for a new bushing.
AKwalor posted 06-26-2004 01:21 PM ET (US)     Profile for AKwalor  Send Email to AKwalor     
I have a 15 sport with a brand new 90 with a 19 pitch aluminum prop. I've got it to max out at 45 on the gps at 5500 rpm but i can't hold it there long because it starts to chine walk to bad and i can't control it. any ideas on how to fix the problem so i can get max speed in the 50's like everyone is talking about and be able to control it.
gtcway posted 06-26-2004 01:36 PM ET (US)     Profile for gtcway  Send Email to gtcway     
I'm not an expert but I think you will need to raise the engine and get a stainless steel prop to maximize performance. When I had my engine mounted at the standard height chine walking was a terrible problem. I couldn't stay at WOT for more than a few seconds before having to slow down.
texas_whaler posted 06-30-2004 08:51 AM ET (US)     Profile for texas_whaler  Send Email to texas_whaler     
This is tripping me out!! I have a 17' Montauk that is rated for like a 100hp motor max!! How the heck are you guys able to run a 90hp motor on a 15' whaler?? What is the max rating??


gtcway posted 06-30-2004 09:25 PM ET (US)     Profile for gtcway  Send Email to gtcway     
The max for a 15' is 70hp.
texas_whaler posted 07-06-2004 11:02 AM ET (US)     Profile for texas_whaler  Send Email to texas_whaler     
Hmmm.. What would happen if I put say a 150 hp motor on my montauk??
gtcway posted 07-06-2004 06:02 PM ET (US)     Profile for gtcway  Send Email to gtcway     
A friend of a friend did that several years ago. I only heard about it but it was fast and unstable. Can you imaging the acceleration with a Johnson 60 deg. 150 on a Montauk :) You could probably jump out of the water.

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