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Author Topic:   180 Dauntless 19-pitch

obxharry posted 05-15-2015 05:44 AM ET (US)
If [the propeller on a Boston Whaler 180 DAUNTLESS is changed to] 19-pitch from 17-pitch, should [the boat] go slower?
Why are people getting more speed out of a Mercury OptiMax 135-HP outboard engine with a higher pitch [propeller]?
[One] would think going to a 16-pitch propeller would give [the boat] more top end speed than going to a 19-pitch from 17-pitch.
jimh posted 05-15-2015 07:01 AM ET (US)
Propellers having more pitch require more force to turn. The outboard engine accelerates to the most speed it can reach to turn a particular load. By varying the propeller pitch, the load on the engine is varied. The greatest boat speed occurs when the propeller pitch is as high as possible (and thus the load is highest) but still permits the engine to accelerate to its full horsepower engine speed range.
obxharry posted 05-15-2015 09:05 AM ET (US)
[If] a 180 Dauntless with Mercury OptiMax 135-HP with 17-pitch [propeller is fitted with a propeller of] 19 [pitch], will [the boat] go faster?
jimh posted 05-15-2015 09:45 AM ET (US)
I recommend you check the Boston Whaler website for any published performance reports for a 180 DAUNTLESS with Mercury 135-HP OptiMax engine. Generally when Boston Whaler publishes a performance report about a particular combination of boat and outboard engine, they test a number of propellers and select the propeller model and propeller pitch that gives the best overall performance.
It is difficult to predict precisely what effect on boat speed will result from changing the pitch of a propeller. Decreasing propeller pitch tends to reduce the load, and a reduced load permits the engine to accelerate to a higher full-throttle engine speed. Increasing propeller pitch has the opposite effect, that is, the load is increased, and the engine may not be able to accelerate to the same speed at full-throttle as before. Exactly how the higher-pitch but slower turning propeller will affect boat speed is difficult to predict. Because testing a propeller is relatively simple, the best method to discover the speed that will result with a particular combination of engine, boat, and propeller is to actually test them on the water.
jimh posted 05-16-2015 09:26 AM ET (US)
ASIDE to OBXHARRY--I deleted the article you posted to an eight-year-old thread you revived because you asked the same questions in that article as you are asking here. Please to do not revive older threads only to ask the same questions you are asking here. You have started this new thread in which you are asking your questions, and it is not necessary to revive threads that have been dormant for many years only to repeat your questions in those dormant threads.

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Author	Topic: 180 Dauntless 19-pitch
obxharry	posted 05-15-2015 05:44 AM ET (US) If [the propeller on a Boston Whaler 180 DAUNTLESS is changed to] 19-pitch from 17-pitch, should [the boat] go slower? Why are people getting more speed out of a Mercury OptiMax 135-HP outboard engine with a higher pitch [propeller]? [One] would think going to a 16-pitch propeller would give [the boat] more top end speed than going to a 19-pitch from 17-pitch.
jimh	posted 05-15-2015 07:01 AM ET (US) Propellers having more pitch require more force to turn. The outboard engine accelerates to the most speed it can reach to turn a particular load. By varying the propeller pitch, the load on the engine is varied. The greatest boat speed occurs when the propeller pitch is as high as possible (and thus the load is highest) but still permits the engine to accelerate to its full horsepower engine speed range.
obxharry	posted 05-15-2015 09:05 AM ET (US) [If] a 180 Dauntless with Mercury OptiMax 135-HP with 17-pitch [propeller is fitted with a propeller of] 19 [pitch], will [the boat] go faster?
jimh	posted 05-15-2015 09:45 AM ET (US) I recommend you check the Boston Whaler website for any published performance reports for a 180 DAUNTLESS with Mercury 135-HP OptiMax engine. Generally when Boston Whaler publishes a performance report about a particular combination of boat and outboard engine, they test a number of propellers and select the propeller model and propeller pitch that gives the best overall performance. It is difficult to predict precisely what effect on boat speed will result from changing the pitch of a propeller. Decreasing propeller pitch tends to reduce the load, and a reduced load permits the engine to accelerate to a higher full-throttle engine speed. Increasing propeller pitch has the opposite effect, that is, the load is increased, and the engine may not be able to accelerate to the same speed at full-throttle as before. Exactly how the higher-pitch but slower turning propeller will affect boat speed is difficult to predict. Because testing a propeller is relatively simple, the best method to discover the speed that will result with a particular combination of engine, boat, and propeller is to actually test them on the water.
jimh	posted 05-16-2015 09:26 AM ET (US) ASIDE to OBXHARRY--I deleted the article you posted to an eight-year-old thread you revived because you asked the same questions in that article as you are asking here. Please to do not revive older threads only to ask the same questions you are asking here. You have started this new thread in which you are asking your questions, and it is not necessary to revive threads that have been dormant for many years only to repeat your questions in those dormant threads.