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billjnh is that 31 mph at 6,000 rpm? If so yes that is not max. I get 31 knots (36 mph) with the weight load you mentioned. Do you fine trim after WOT.
I assume motor mounted correctly (up) and the stainless Vengeance prop.
No that's at 5,000 rpm with with motor trimmed. Going above 5000 doesn't seem to increase speed, yes on the vengeance prop. Motor is. Mounted one hole from the lowest hole if you are looking at it.
EJO wrote:
gypsmjim
I did go ahead and bought a Doel Fin set.
The instructions are very vague as they don't tell you where to mount them on your anti cavitation plate.
As an engineer I wanted to know where to put these fins on the plate as the plate on the 60HP EPI 4 stroke is a lot longer than the Doel fins. No where in their mounting instruction do they give this info so I called customer service and was told to center the foils over the C/L of the prop equal to where the foil straight edge angles back to the cav.plate.
That said I did so and ended up with longer out of the hole shot with higher bow rise (engine tucked in all the way) same top WOT speed except much more prone to porpoising.
This was with 4 adults (800+lbs crew and all) the standard 3 bladed Vengeance SS prop. Yes I could plane at slightly lower speed but with two adult women on the bow cushion I felt like the bow was riding to high.
I will remove the $28 "fix" as it didn't really make it "perfect" and I didn't like the way the boat was riding or porpoising.
Pardon my tardy reply, but we have been on vacation again. Put a lot of gas thru the new Montauk these past few weeks. Our other boats are feeling neglected.....LOL.
As I said before, this is the forth boat to sport a DoelFin. The first 2 were purchased from Mr Doelcher himself. I can't remember what the old installation instructions were, and subsequent installations were done without even reading the new manuals.
ALL my fins were mounted as far back as possible on the anti-ventilation plate. If you have a worse hole shot, more bow rise and porpoising, my guess would be the fin is in the wrong place, since yours got worse and mine got better.
My engine is mounted in the 3rd hole up, and the prop is the std. Vengeance, all as it came from the factory.
As a rule, I don't like WOT. With a 450 lb. load and 2 full tanks our Montauk's sweet spot is about 4000-4500 RPM. With a slight amount of trim this runs at about 23 mph GPS. WOT with a fair amount of trim I get about 5800 rpm and 33 mph, which is close to the published specs. I have NEVER seen porpoising at ANY conditions, with or without the fin.
Much of the reason for discussing speed performance, WOT rpms, prop model and size and engine height is not for top speed. When all of these pieces are"dialed in" the engine will be performing correctly at all speeds.
We want to avoid a situation where the boat is running like a car racing up a steep hill in either 1st gear or lugging in 5th.
Phil T wrote:
Much of the reason for discussing speed performance, WOT rpms, prop model and size and engine height is not for top speed. When all of these pieces are"dialed in" the engine will be performing correctly at all speeds.
We want to avoid a situation where the boat is running like a car racing up a steep hill in either 1st gear or lugging in 5th.
That's exactly true. As the "experts" suggest, and from my own personal experience, if WOT provides an rpm that is right at the engine's max spec, "performance" will be optimum.
gypsmjm
i agree with your sweet spot statement that is where I like to run too @ 21knts (23.5 mph)
I also agree with the statement that the installation I did (following Doel factory recommendations) incorrect. I hate to drill 4 new holes but will move them aft, as now they are about 2 " forward of the back end of the plate.
We'll see this weekend.
I ran the boat more than 90 miles during the 2 day weekend and we had a blast in a poker run and just cruising up and down the Eastern Lake Michigan shore.
During our usual week vacation on the Saint Lawrence River in early July we logged ONLY 127 miles. The weather was iffy (cold some days) and rain was frequent. We usually run a good 300 miles on our jetski in good weather. The wife was glad we took the new Whaler instead...
Sorry about having to drill more holes. At least you are not installing trim tabs in the hull with 16 screw holes. If it turns out you really don't like the tab, filling the holes with small SS or poly bolts will make them hardly noticeable.
Please report back on your performance. I'll be glad to help if I can.
On a side note, the weather was splendid today so we took out our 65 year old wood Lyman, with her 64 year old Evinrude outboard. Had some engine problems (I'm also that age and I too get finicky at times), but she managed to get us home safe as sound.
EJO wrote:
gypsmjm
i agree with your sweet spot statement that is where I like to run too @ 21knts (23.5 mph)
I also agree with the statement that the installation I did (following Doel factory recommendations) incorrect. I hate to drill 4 new holes but will move them aft, as now they are about 2 " forward of the back end of the plate.
We'll see this weekend.
I ran the boat more than 90 miles during the 2 day weekend and we had a blast in a poker run and just cruising up and down the Eastern Lake Michigan shore.
Since you didn't reply, I was wondering how things came out. Hope you made an improvement after you moved the fin...
