CONTINUOUSWAVE

[Moderator's note: separated from another thread which contained too many topics for useful discussion.]

Q1: what brand, model, diameter, and pitch propeller is appropriate for use on a c.1979 MONTAUK 17 that has been re-powered with an E-TEC 115-HP engine (of unspecified model).

ASIDE: I would love to reach a top speed of 50-MPH, but I would be happy with 42-MPH.

jimh wrote:Q1: what brand, model, diameter, and pitch propeller is appropriate for use on a c.1979 MONTAUK 17 that has been re-powered with an E-TEC 115-HP engine (of unspecified model).

There are two distinctly different E-TEC engines of 115-HP: an in-line three-cylinder, and a V-block 60-degree four-cylinder. Please identify which engine you are asking about. Give the full engine model designator.

Clear identification of the engine will help readers give better suggestions about propeller selection.

IMPORTANT
The maximum rated horsepower for a c.1979 MONTAUK 17 boat is 100-HP. Before choosing re-power the boat with a 115-HP engine and exceed the rated horsepower, you should carefully consider the implications:

• the boat is now 46-years old, and as you previously described has significant damage at the transom and has been neglected; and,
• although there is no federal regulation that prevents you from powering the boat above its manufacturer's rated maximum power, there could be local or state regulations that forbid using the boat on those waters

There is no reasonable basis to expect that as the boat sat neglected for much of its 46-years the strength of the hull and transom magically increased enough that it could support a more powerful (and likely heavier) outboard engine than originally specified by the manufacturer.

In addition to possible violation of state or local laws, powering the boat above its manufacturer's rated maximum may required you to purchase liability insurance that explicitly declares the boat has such excess power and the insurer is aware of this and condones it. Typically boat insurance issuers will require additional costs to insure boats that are over-powered.

In the event of any legal proceedings as a result of an accident with the boat, the use of an engine that exceeds the rated maximum could put you in an unfavorable position in a dispute.

The [used outboard engine] I bought is a 2008 Evinrude E115DSLSCR, 20-shaft, Saltwater edition, that has 213 hours, and 30-percent were below 2000rpm.

I have faith in the indestructible spirit of the Montauk, and in the repairs that I have and I will have made.

Additionally, the person who used and abused the boat prior to gifting it to me ran a 115-HP [two-stroke-power-cycle engine] and he ran [that boat] in the water for years in a neglected state.

I am hoping that someone running the exact same setup as me, with an early model 17 MONTAUK, and a Evinrude 115 E-TEC will tell me the propeller that they run.

Also, I want to know the fuel economy.

malcHILL wrote:The [used outboard engine] I bought is a 2008 Evinrude E115DSLSCR, 20-shaft, Saltwater edition…

Don’t get too excited. The only unique feature of the 2008 “Saltwater” edition is that it is painted white, not blue.

The model designation agrees with your description, except for that trailing “R.” The last letter is to designate the production run sequence, and indicating an “R” sequence suggests it was after A, B, C, D, and so on. That seems a bit too far down the list. Perhaps you could check that again.

UPDATE: after searching for mentions of production sequence “R”, I found other E-TEC engines model codes from 2008 used that letter, too.

The "saltwater edition" means [the white color of the engine] is matching the boat, and the various other Evinrude and E-TEC engines my dad and uncle own. It will fit in with the clan.

It sounds like you have the E-TEC V4 engine with 115-HP. At 390-lbs it is a heavier engine than the three-cylinder 90-HP 335-lbs engine that is often used for re-powering a MONTAUK 17. The boat trim will be down-by-the-stern. You are over the rated power. But there is no point talking about that, because you already bought the engine.

For optimum performance, the full-throttle engine speed of a 2008 E-TEC 115-HP should be in the range of 5,600 to 5,700-RPM.

The gear ratio should be 2.25:1 from what information I can find.

In a prior discussion, a 1987 MONTAUK 17 with an E-TEC 90 reported a top speed of 42.5-MPH using a 17-pitch propeller with minimal gear and one person aboard. We can estimate the hull weight was 1,800-lbs (using the Crouch speed prediction formula).

Using that data we can predict the boat speed for 115-HP and 1,860-lbs will be 47-MPH.

On that basis, a propeller pitch for a 2.25:1 gear ratio and engine speed 5,700-RPM that will produce 47-MPH (allowing for a SLIP of 10) will be around 21-inches. For all-round use a good three-bladed propeller is an excellent choice. Be sure to get a propeller that fits the gear case diameter, the propeller aperture space, the number of splines on the propeller shaft, and has the correct thrust washers or spacers if not an Evinrude propeller.

The most important element in this case is getting the full-throttle engine speed into the recommended (and rather narrow) optimum range. If the 21-pitch is too much and the engine cannot accelerate into the optimum engine speed range, drop to a 19-pitch.

The speed is all about power-to-weight ratio, and there is no way to know what your particular 46-year-old hull is going to weigh when you get done with all the repairs. Old boats to not tend to become lighter as they age and acquire significant additions of new laminate and other repairs. Also, crew weight is influential on boats, and particularly on smaller and lighter boats. So if you are going to be out boating with four people that each weigh over 200-lbs, you won't get the same speed as if the boat had one person that weighs 175-lbs aboard.

Thank you! Can you provide the place where you got 2:25 ratio for the motor? From what I've found this model has 2:00:1 ratio for the 20" shaft