170 DAUNTLESS, 100-HP; Propeller

Optimizing the performance of Boston Whaler boats
floris van den berg
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Joined: Sat Apr 08, 2017 2:41 am

170 DAUNTLESS, 100-HP; Propeller

Postby floris van den berg » Sun Nov 19, 2017 4:25 pm

I recently bought a used 2014 Boston Whaler 170 Dauntless with a Mercury 100-HP four-stroke-power-cycle engine. The engine is very big in size compared to the Yamaha F70 on my other boat.

The Mercury 100-HP carries a TROPHYplus four-blade stainless steel propeller with 17-pitch. Acceleration is very good and the engine runs up to about 5,900-RPM at a boat speed of 33 nautical-miles-per-hour.

What type of three-blade propeller is standard for this boat?

What are the characteristic differences between three-blade and four-blade propellers?

jimh
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Re: 170 DAUNTLESS, 100-HP; Propeller

Postby jimh » Sun Nov 19, 2017 6:05 pm

Four-blade propellers tend to have more blade area than three-blade propellers, causing them to create a higher load on the engine trying to turn them than would be created by a three-blade of similar diameter and pitch.

Jefecinco
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Re: 170 DAUNTLESS, 100-HP; Propeller

Postby Jefecinco » Sun Nov 19, 2017 7:36 pm

Four blade propellers also provide stern lift and allow some boats to remain on plane at lower speeds and they can provide faster acceleration and allow the boat to achieve plane more quickly. Top speed is often slightly lower with a four blade. On our previous boat, a 1999 Dauntless 16 with a 115 HP engine, we preferred the better performance of a four blade even with the slight loss of top speed. We, like most boat owners, seldom operated our Dauntless at top speed.
Butch

floris van den berg
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Joined: Sat Apr 08, 2017 2:41 am

Re: 170 DAUNTLESS, 100-HP; Propeller

Postby floris van den berg » Mon Nov 20, 2017 3:07 am

Thanks for your insight in this.

I try to figure out how the boat performs compared to what I am used to. I have had quite a few boats in the past--all aluminum and with Yamaha's. What I notice is that the mentioned F70 Yamaha performs better in the high RPM--what I mean is that you get a lot more speed in the higher RPM--while the Dauntless does most between the 4000 and 5000 RPM. I like that, too, but don't know if that is because of the four-blade or because of the Mercury engine.

and Jefecinco--cruising the Dauntless at 4000 RPM and about 24-nautical-miles-per-hour is a very nice speed and efficient btw :)
Last edited by floris van den berg on Mon Nov 20, 2017 4:52 am, edited 1 time in total.