## 13-footer with 40 HP

Optimizing the performance of Boston Whaler boats
joemahoney79
Posts: 6
Joined: Fri May 07, 2021 1:53 pm

### 13-footer with 40 HP

Q1: What propeller is the ideal propeller for a 1988 SPORT 13 with a 1988 Yamaha 40-HP two-stroke-power-cycle engine with three cylinders?

I have tried the various prop calculators.

I am prepared to do a full RPM test.

I hope [some advice on a propeller contributed in reply to this post] might save me time.

Thanks

jimh
Posts: 9240
Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula
Contact:

### Re: 13-footer with 40 HP

Q2: What is the GEAR RATIO of your engine?

Q3: What is the manufacturer's recommended full-throttle engine speed range?

Q4: Do you have a TACHOMETER for the engine?

Q5: Do you have a means of measuring BOAT SPEED?

Q6: Do you have any data about the boat performance?

Q7: What will be the total weight of the boat, engine, gear, and passengers for normal operation?

jimh
Posts: 9240
Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula
Contact:

### Re: 13-footer with 40 HP

joemahoney79 wrote:I have tried the various prop calculators.

A propeller calculator is not an oracle. It just computes a parameter based on other parameters you give as input.

A propeller calculator cannot be used to select a propeller for a particular boat and engine combination until the boat speed at full throttle has been estimated or calculated or taken from observations made by others, until the engine speed at full-throttle is known, and until the gear ratio of the engine is known.

Phil T
Posts: 1731
Joined: Thu Oct 22, 2015 6:08 pm
Location: Currently Kentucky

### Re: 13-footer with 40 HP

From owners with the Yamaha 40hp and the classic 13' Sport, the list of recommended props include:

10.5 x 13 aftermarket
10.5 x 12 Yamaha Performance/Turbo Hot Shot

The engine should be mounted "1 hole up" so the top engine bolts are in the 2nd hole counting down from the top.

As for performance, running solo, light, no gear, smooth bottom paint, on calm water, should see 34-36 mph.
1992 Outrage 17
2019 E-TEC 90
Member since 2003

joemahoney79
Posts: 6
Joined: Fri May 07, 2021 1:53 pm

### Re: 13-footer with 40 HP

@Phil T thanks for the help. When you say 1 hole up on the engine mount wouldn't that mean that bracket would not bottom out on the top of the transom? The boat originally came with a smaller Honda 4 stroke and the bolt holes are totally different. I am filling the old holes with stacked teak plugs and filling/fairing. Going to be drilling new holes to mount the Yamaha.

Phil T
Posts: 1731
Joined: Thu Oct 22, 2015 6:08 pm
Location: Currently Kentucky

### Re: 13-footer with 40 HP

1992 Outrage 17
2019 E-TEC 90
Member since 2003