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Author Topic:   17' Montauk 90 hp 4-stroke 2003
Donzi posted 05-03-2004 04:53 PM ET (US)   Profile for Donzi   Send Email to Donzi  
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,
Dan
Barney posted 05-03-2004 06:12 PM ET (US)     Profile for Barney  Send Email to Barney     
I don't think it would be necessary. Give the factory equipment a try first. Jim
Donzi posted 05-04-2004 07:57 AM ET (US)     Profile for Donzi  Send Email to Donzi     
Jim: thanks for the reply. I will test out the factory prop this weekend.
thanks,
Dan


jimh posted 05-04-2004 08:38 AM ET (US)     Profile for jimh  Send Email to jimh     
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.
Peter posted 05-04-2004 09:17 AM ET (US)     Profile for Peter  Send Email to Peter     
Jim, what about "stern lifting" versus "bow lifting" propellers of equal pitch? Couldn't that have some impact on porpoising?
Donzi posted 05-04-2004 03:07 PM ET (US)     Profile for Donzi  Send Email to Donzi     
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.
AQUANUT posted 05-04-2004 10:08 PM ET (US)     Profile for AQUANUT  Send Email to AQUANUT     
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.
Chuck Tribolet posted 05-05-2004 12:35 AM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
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.


Chuck

jimh posted 05-05-2004 08:48 AM ET (US)     Profile for jimh  Send Email to jimh     
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.

Barney posted 05-05-2004 08:59 AM ET (US)     Profile for Barney  Send Email to Barney     
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
Vic Holmstrom posted 05-05-2004 09:16 AM ET (US)     Profile for Vic Holmstrom  Send Email to Vic Holmstrom     
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.

Donzi posted 05-05-2004 09:21 AM ET (US)     Profile for Donzi  Send Email to Donzi     
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,
Dan
Knot at Work posted 05-05-2004 10:19 AM ET (US)     Profile for Knot at Work  Send Email to Knot at Work     
18 inches here... yes the prop

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