170 MONTAUK: Whaler Factory Performance v. Actual

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Author Topic:   170 MONTAUK: Whaler Factory Performance v. Actual

AZdave posted 03-06-2014 04:22 PM ET (US)
We had our 170 Montauk out yesterday under calm conditions and a 75 degree temperature. The lake has an elevation of about 1500 ft. The boat has the middle version of the Mercury 90 hp four stroke engine. That is, it has a Yamaha powerhead with fuel injection. Whaler's website says it should go 43 mph at 5800 rpm. We got no more than 37 mph at 5600 rpm. We had about 150 lbs more crew, 10 gallons more fuel, three batteries and a bow mount trolling motor. Is that difference in top speed reasonable? Also the boat has the stock stainless prop, and the motor is mounted one hole above the bottom. I know to trim out for maximum speed, but the boat shows significant porpoising when trimmed out for maximum rpm. Thanks.. Dave
Tom W Clark posted 03-06-2014 04:32 PM ET (US)
The added weight accounts for ~4 MPH decrease.
The smooth, fresh water and 1500 feet of elevation account for the other 2 MPH. I'd say it sounds about right.
If the propeller is a Laser II, the motor should be raised on the transom at least one more bolt hole. That alone will reduce or eliminate the porpoising and increase the top speed.
AZdave posted 03-06-2014 10:50 PM ET (US)
Thanks Tom. I'll see about setting up a lifting frame. The propeller is an 18 pitch Vengeance.
Tom W Clark posted 03-06-2014 10:57 PM ET (US)
Well, then try a 13-1/4" x 20" Laser II. It will be a much better fit on that boat/motor combination.
Tom W Clark posted 03-06-2014 10:59 PM ET (US)
Actually, a 13-1/4" x 19" Stiletto Advantage will perform as well or better than the Laser II and will cost significantly less too.
tedious posted 03-07-2014 08:07 AM ET (US)
Dave, if you have the boat on a trailer, you don't need a lifting frame. Just lower the front of the trailer all the way on the jack, then put blocks under the skeg. Take the top mounting bolts out, and loosen the lower ones, and then raise the jack to lift the motor. Pretty simple, one person operation.
Tim
AZdave posted 03-07-2014 10:31 AM ET (US)
That's a great idea, Tim. Are you pretty sure that the skeg will hold the 400 lb weight of the motor? I might still round up a couple of friends to balance it during the operation.
Tom W Clark posted 03-07-2014 10:44 AM ET (US)
Yes, the skeg is more than strong enough.
Yes, get some friends to help; the Mercurys does not use a lower slot so all four bolts need to be removed to move the motor.
I've done this several times. The last time I moved a Mercury 90, last summer, I got two neighbors to help. Use a strap or line between the stern eyes and around the back of the motor, as a safety in case your helpers loose control.
Block the trailer wheels well so it cannot roll.
AZdave posted 03-07-2014 10:54 AM ET (US)
That looks easy to do. I can't believe that it never occurred to me to treat the trailer and jack as a lever. I will give an update. Thanks to you both.

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Author	Topic: 170 MONTAUK: Whaler Factory Performance v. Actual
AZdave	posted 03-06-2014 04:22 PM ET (US) We had our 170 Montauk out yesterday under calm conditions and a 75 degree temperature. The lake has an elevation of about 1500 ft. The boat has the middle version of the Mercury 90 hp four stroke engine. That is, it has a Yamaha powerhead with fuel injection. Whaler's website says it should go 43 mph at 5800 rpm. We got no more than 37 mph at 5600 rpm. We had about 150 lbs more crew, 10 gallons more fuel, three batteries and a bow mount trolling motor. Is that difference in top speed reasonable? Also the boat has the stock stainless prop, and the motor is mounted one hole above the bottom. I know to trim out for maximum speed, but the boat shows significant porpoising when trimmed out for maximum rpm. Thanks.. Dave
Tom W Clark	posted 03-06-2014 04:32 PM ET (US) The added weight accounts for ~4 MPH decrease. The smooth, fresh water and 1500 feet of elevation account for the other 2 MPH. I'd say it sounds about right. If the propeller is a Laser II, the motor should be raised on the transom at least one more bolt hole. That alone will reduce or eliminate the porpoising and increase the top speed.
AZdave	posted 03-06-2014 10:50 PM ET (US) Thanks Tom. I'll see about setting up a lifting frame. The propeller is an 18 pitch Vengeance.
Tom W Clark	posted 03-06-2014 10:57 PM ET (US) Well, then try a 13-1/4" x 20" Laser II. It will be a much better fit on that boat/motor combination.
Tom W Clark	posted 03-06-2014 10:59 PM ET (US) Actually, a 13-1/4" x 19" Stiletto Advantage will perform as well or better than the Laser II and will cost significantly less too.
tedious	posted 03-07-2014 08:07 AM ET (US) Dave, if you have the boat on a trailer, you don't need a lifting frame. Just lower the front of the trailer all the way on the jack, then put blocks under the skeg. Take the top mounting bolts out, and loosen the lower ones, and then raise the jack to lift the motor. Pretty simple, one person operation. Tim
AZdave	posted 03-07-2014 10:31 AM ET (US) That's a great idea, Tim. Are you pretty sure that the skeg will hold the 400 lb weight of the motor? I might still round up a couple of friends to balance it during the operation.
Tom W Clark	posted 03-07-2014 10:44 AM ET (US) Yes, the skeg is more than strong enough. Yes, get some friends to help; the Mercurys does not use a lower slot so all four bolts need to be removed to move the motor. I've done this several times. The last time I moved a Mercury 90, last summer, I got two neighbors to help. Use a strap or line between the stern eyes and around the back of the motor, as a safety in case your helpers loose control. Block the trailer wheels well so it cannot roll.
AZdave	posted 03-07-2014 10:54 AM ET (US) That looks easy to do. I can't believe that it never occurred to me to treat the trailer and jack as a lever. I will give an update. Thanks to you both.