Thread subject: Whaler Central - Boston Whaler Boat Information and Photos :: 75 etec performance on a classic Montauk
Posted by jcdawg83 on 10/20/16 - 1:00 PM
#1
I have a
1977 Montauk with a 75hp etec running a 15" pitch aluminum prop. The hull is painted (not by me, was painted when I got it because it was used in salt water and left tied at a dock for up to a week at the time) and the boat has a t top.
My top speed is around 35-36 mph at 5300 rpm, does that sound right or should it be higher? I know the bottom paint cuts a little speed and the t top creates some wind resistance. I'm getting that speed with only me in the boat and about 15 gallons of fuel.
I don't know if that speed is about what I should expect or should it be higher.
(please follow guideline #1 at the top of this page)
Edited by Joe Kriz on 10/20/16 - 1:17 PM
Posted by jcdawg83 on 10/20/16 - 1:22 PM
#3
It is mounted with a 4" jack plate, the cavitation plate is about an inch and a half above the bottom of the hull.
Edited by jcdawg83 on 10/20/16 - 1:23 PM
Posted by Phil T on 10/20/16 - 1:55 PM
#4
Given the top and paint, you are pretty well dialed in. WOT is 5500 rpms.
i would try raising the engine one set of holes and observe the results. It may give you an extra 125 rpm, 1 mph.
Posted by tedious on 10/20/16 - 2:29 PM
#5
That speed sounds about right for your setup. You could probably squeeze a little more out by raising the motor more and going to a better, stainless steel prop. With 4" setback and a good prop, you should be able to come up a bit. But you're only going to gain a little - not sure if it is worth it. Put a 90HO or a Honda 100 on there if you want to go faster, but still stay within the hull rating.
Tim
Posted by jcdawg83 on 10/21/16 - 5:35 AM
#6
Thanks everyone. I looked at the motor last night and it is already mounted all the way up. I guess I'm getting all I can get. I had a 13" pitch prop but it was over revving, about 6000 rpms, so I went to the 15". I've thought about a 15" stainless but I don't think I'd get much more out of it.
I don't do much WOT running anyway and the cruising performance is great. It does about 23 mph at 3500 rpms and uses so little fuel I think it might be solar powered in some way. Overall, I've been very pleased and I got a great deal on the motor.
Posted by Phil T on 10/21/16 - 5:55 AM
#7
Keep in mind performance is not necessarily a result of pitch. Propeller design is very sophisticated and sizing is not universal.
Generally speaking stainless steel propellers perform better than aluminum. As for size, it is wholly dependent on the make and model you choose.
I think staying with the current prop is economically sound.
Posted by tedious on 10/21/16 - 11:19 AM
#8
jcdawg83 wrote:
I don't do much WOT running anyway and the cruising performance is great.
I ended up in the same situation on my 15 - may be giving away a tiny bit of ultimate top speed, but the instant acceleration, great handling, and ability to carry heavy loads more than make up for it. It's all about matching the setup to what you need!
Tim