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Author Topic:   160 DAUNTLESS, 90-HP Four-cycle

Bayguy posted 08-08-2008 06:55 AM ET (US)
I recently repowered my 04' [probably means 2004 model year] 16 D [probably means Boston Whaler 160 DAUNTLESS] with a new Yamaha 90 four-cycle motor with stainless steel propeller. The boat's performance is lack luster. With only two aboard, a light load, and half-full tank of gas my top speed is only 30-MPH. Is this normal?
Casco Bay Outrage posted 08-08-2008 09:49 AM ET (US)
It would help to know
Make, model and size of propeller. There are thousands of them and each are different.
Where is the engine mounted on the transom. More specifically, where is the anti-cavitation plate in relation to the bottom of the hull? Below, at or above. If above, how much?
With this information we can give you propeller and mounting advice.
boatdryver posted 08-09-2008 09:50 AM ET (US)
Bayguy, it would also be helpful to report your rpm at wide open throttle and use or borrow a gps to determine your true speed.
If you just repowered and bought the motor from a dealer, I'd take the problem back to him or her immediately. They will normally be very helpful.
JimL
jimh posted 08-09-2008 11:29 AM ET (US)
Generally speaking a 16-foot Boston Whaler boat with a 90-HP motor ought to be able to obtain a top speed greater than 30-MPH. Using Crouch's formula for predicting the performance of moderate planing hull boats, to obtain only a 30-MPH top speed with a typical Boston Whaler hull and 90-HP, the combined weight of the boat, motor, crew, and gear would have to be about 3,240-lbs.
According to some literature, the 160 DAUNTLESS hull weighs about 1,500-lbs. If we allow 500-lbs for the motor and gear, we have a 2,000-lbs boat weight. Add two adults, and we should not have a total weight much more than 2,500-lbs.
Using a total weight of 2,500-lbs, a constant or hull factor of 180 (which is typical for Boston Whaler boats), and 90-HP, the predicted top speed of your boat should be around 34-MPH.
It is not unusual for other factors to influence the top speed of a boat besides weight and horsepower. Weather conditions, sea conditions, operating adjustment, and of course propeller selection are all very influential.
http://continuouswave.com/cgi-bin/crouchcalc.pl
Tom W Clark posted 08-09-2008 11:47 AM ET (US)
Jim has predicted what should be the top speed of the Dauntless 16 with 90 HP using a theoretical formulaic approach. One can also use an anecdotal approach.
The Dauntless 16 with a 90 HP Mercury four stroke is reported by the factory to do about 40 MPH, so only 30 MPH would seem to be quite anemic.
http://www.whaler.com/Rec/pdfs/160DauntlessEng.pdf
Perry posted 08-09-2008 12:53 PM ET (US)
I used to own a 160 Dauntless with a 90 HP 4 stroke motor and it used to top out at 39.5 MPH at 6000 RPM. So I agree that your boat should perform better than 30 MPH.
How's that for first hand information?
jimh posted 08-09-2008 08:54 PM ET (US)
In my analysis I used a total weight of 2,500-lbs. In the Boston Whaler test data the total weight is given as 2,449-lbs. Not a bad estimate on my part, I'd say.
In the Whaler test data we get 40.7-MPH out of 90-HP. This implies the boat has a hull factor constant of 212. To push this boat to 30-MPH would probably take only 50-HP.

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Author	Topic: 160 DAUNTLESS, 90-HP Four-cycle
Bayguy	posted 08-08-2008 06:55 AM ET (US) I recently repowered my 04' [probably means 2004 model year] 16 D [probably means Boston Whaler 160 DAUNTLESS] with a new Yamaha 90 four-cycle motor with stainless steel propeller. The boat's performance is lack luster. With only two aboard, a light load, and half-full tank of gas my top speed is only 30-MPH. Is this normal?
Casco Bay Outrage	posted 08-08-2008 09:49 AM ET (US) It would help to know Make, model and size of propeller. There are thousands of them and each are different. Where is the engine mounted on the transom. More specifically, where is the anti-cavitation plate in relation to the bottom of the hull? Below, at or above. If above, how much? With this information we can give you propeller and mounting advice.
boatdryver	posted 08-09-2008 09:50 AM ET (US) Bayguy, it would also be helpful to report your rpm at wide open throttle and use or borrow a gps to determine your true speed. If you just repowered and bought the motor from a dealer, I'd take the problem back to him or her immediately. They will normally be very helpful. JimL
jimh	posted 08-09-2008 11:29 AM ET (US) Generally speaking a 16-foot Boston Whaler boat with a 90-HP motor ought to be able to obtain a top speed greater than 30-MPH. Using Crouch's formula for predicting the performance of moderate planing hull boats, to obtain only a 30-MPH top speed with a typical Boston Whaler hull and 90-HP, the combined weight of the boat, motor, crew, and gear would have to be about 3,240-lbs. According to some literature, the 160 DAUNTLESS hull weighs about 1,500-lbs. If we allow 500-lbs for the motor and gear, we have a 2,000-lbs boat weight. Add two adults, and we should not have a total weight much more than 2,500-lbs. Using a total weight of 2,500-lbs, a constant or hull factor of 180 (which is typical for Boston Whaler boats), and 90-HP, the predicted top speed of your boat should be around 34-MPH. It is not unusual for other factors to influence the top speed of a boat besides weight and horsepower. Weather conditions, sea conditions, operating adjustment, and of course propeller selection are all very influential. http://continuouswave.com/cgi-bin/crouchcalc.pl
Tom W Clark	posted 08-09-2008 11:47 AM ET (US) Jim has predicted what should be the top speed of the Dauntless 16 with 90 HP using a theoretical formulaic approach. One can also use an anecdotal approach. The Dauntless 16 with a 90 HP Mercury four stroke is reported by the factory to do about 40 MPH, so only 30 MPH would seem to be quite anemic. http://www.whaler.com/Rec/pdfs/160DauntlessEng.pdf
Perry	posted 08-09-2008 12:53 PM ET (US) I used to own a 160 Dauntless with a 90 HP 4 stroke motor and it used to top out at 39.5 MPH at 6000 RPM. So I agree that your boat should perform better than 30 MPH. How's that for first hand information?
jimh	posted 08-09-2008 08:54 PM ET (US) In my analysis I used a total weight of 2,500-lbs. In the Boston Whaler test data the total weight is given as 2,449-lbs. Not a bad estimate on my part, I'd say. In the Whaler test data we get 40.7-MPH out of 90-HP. This implies the boat has a hull factor constant of 212. To push this boat to 30-MPH would probably take only 50-HP.