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ContinuousWave: Whaler Performance
17' Montauk 90 hp 4-stroke 2003
|Author||Topic: 17' Montauk 90 hp 4-stroke 2003|
posted 05-03-2004 04:53 PM ET (US)
Just purchased a Montauk and wondered if the Vengence 18" prop is worth changing to increase top speed. I had one on my Donzi and it seemed to porpoise really bad at mid-range speeds. I went to a Turbo prop and it worked perfect at all speeds.
thanks for your input,
posted 05-03-2004 06:12 PM ET (US)
I don't think it would be necessary. Give the factory equipment a try first. Jim
posted 05-04-2004 07:57 AM ET (US)
Jim: thanks for the reply. I will test out the factory prop this weekend.
posted 05-04-2004 08:38 AM ET (US)
I don't think the choice of propeller can really induce porpoising. The oscillating pitching of the boat is generally a result of trim, speed, sea conditions, and weight distribution, not propeller pitch.
posted 05-04-2004 09:17 AM ET (US)
Jim, what about "stern lifting" versus "bow lifting" propellers of equal pitch? Couldn't that have some impact on porpoising?
posted 05-04-2004 03:07 PM ET (US)
Jim: for whatever reason, the Vengence did not work well on my Donzi at a certain mid-range. Trimming the motor all the way down at that speed was the only thing that seemed to eliminate the porpoising. I did not have the problem when I switched to a Turbo prop. I guess it is not an issue anymore since I joined the Boston Whaler family.
posted 05-04-2004 10:08 PM ET (US)
it has been my experience, and what I have learned from mercury marine proping techniques fro mercury outboard engines video...that porpoising can be a result of proping.
posted 05-05-2004 12:35 AM ET (US)
I've been on a 2003 Montauk with the 4-stroke 90 and that
prop, and it seemed to work really well. It's almost as
fast as my 1998ish Montauk with a two-stroke 90, and rides
better. I did an 80 nm trip in company with this boat last
Friday, and didn't see any propoising.
If ain't broke, don't fix it.
posted 05-05-2004 08:48 AM ET (US)
Peter, Aquanut--Propeller designs which produce things like bow lift characteristic having an affect on the tendency to porpoise does sound reasonable—and something I had not considered. I guess my boats don't go fast enough to warrant more exotic propellers!
One of the reason that many of these fancier propeller designs are not made in smaller pitches is that you need the boat to be going 40-MPH before you notice the effects.
By the way, I am confused about the initial question. The test data I am seeing at Boston Whaler shows the 170 Montauk with 4-stroke 90-HP is delivered with
13-1/8 X 16 Vengeance (stainless steel three blade)
propeller, so where did Donzi get the "Vengence (sic) 18" prop" ?
Was Donzi's boat delivered with a different propeller than stock?
Must assumption with the boat/motor/propeller combinations delivered from the factory is that these were decided upon as a result of testing, and therefore they represent good choices. At least, a good or best choice from among the Mercury line of propellers, but since Mercury propellers are among the best and certainly have the widest choice, that is a reasonable conclusion.
posted 05-05-2004 08:59 AM ET (US)
jimh, Strange testing on the Whaler website. You are correct the test data shows a 16" prop. However I believe from past discussions here that the current 90 4-strokes are delivered with an 18" prop. At least Knot-at-Work's, Maximus' and mine to name a few also were delivered that way. JimB
posted 05-05-2004 09:16 AM ET (US)
I believe I read somewhere on this site that about a year ago Mercury changed the gear ratio on the 90 4 stroke from 2.07 to 2.33. At that time they probably changed from the 16" to the 18" pitch vengance.
It is surprising that whaler ran the test with the new gear ratio and the 16" prop, causing the engine to rev to 6200. Perhaps they would get better and quieter results by re-running the test with the 18" prop.
posted 05-05-2004 09:21 AM ET (US)
I am 95% sure my 2003 Montauk has a 18" Vengence on the 90hp 4-stroke, but I will recheck it tonight.
thanks for all your input,
|Knot at Work||
posted 05-05-2004 10:19 AM ET (US)
18 inches here... yes the prop
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