CONTINUOUSWAVE

Hey everyone, first time Boston Whaler boat owner here and new to this forum. I just purchased a 1986 [11-footer that] was owned by the Canadian Coast Guard and was well used. I have cleaned up the 11-footer, and I need an engine for it.

How much horsepower is safe for a tiller engine?

I believe the engine should be a short shaft. I want to keep down weight. I was thinking a two-stroke-power-cycle Yamaha 15-HP.

Tell me what you guys run on a 11-foot Whaler. Thanks.

For 11-foot hulls with tiller steering the maximum horsepower is 10-HP. See

http://continuouswave.com/whaler/refere ... #hulls9-17

You will need an outboard engine with a 15-inch shaft length; the choices are limited in that configuration.

Thanks Jim. I see the sport model goes up to 20-HP. Is this due to weight distribution since you are operating a bit forward?

Or is the boat more squirrely with the operator in back with a tiller?

I am trying to get some more speed when I re-power my boat, and was hoping I could safely put a 15 hp Yamaha on the 11-footer.

I have watched some YouTube videos with more HP, but they don't discuss the handling or weight, just going fast in a straight line.

On my 1974 11-footer I have a Mercury 15-HP FOURSTROKE short shaft engine--perfect for me. The boat would not plane with a 1978 Mercury 9.8-HP two-stroke and my 225-lbs.

Rockman wrote:I see the sport model goes up to 20-HP. Is this due to weight distribution since you are operating a bit forward?

Or is the boat more squirrely with the operator in back with a tiller?

The inferences you make are reasonable inferences in my opinion, but I do not have any particularly special knowledge to share with you. Exactly what methods were used to derive the maximum horsepower ratings for different types of engine steering are unknown to me.

Apparently there [are] federal regs that the manufacturers use to derive the rating differences for tiller steer versus remote steering.

https://www.law.cornell.edu/cfr/text/33/183.53

The horsepower rating under federal regulations is described in an older article in REFERENCE published about 13 years (2004) ago and written by me. See

Maximum Rated Horsepower
http://continuouswave.com/whaler/reference/ratedHP.html

As mentioned in the article, it is typical for Boston Whaler to give their boats a rating that is below the maximum rating allowed by the federal regulation method of calculating the maximum horsepower.

Also, as the article mentions, you can install an engine with more horsepower than the rating as far as the Coast Guard is concerned, but local regulations may more strictly enforce the federal maximum rating or the manufacturer's stated maximum.

The federal method of rating for maximum power for an 11-footer would be as follows:

Length = 11-feet 4-inches, or 11.33-feet
Beam at transom or in aft half of boat = 5-feet

Thus length x beam = 11.33 x 5 = 56.65 = the FACTOR

Since the factor is greater than 52, we cannot use the table. We then follow the directions, looking for the particular qualifiers. For the case for tiller steering, the applicable factors will be

--If factor is over 52.5

--the boat has no remote steering, or

--less than 20″ transom height.

Now we compute the federal maximum horsepower according to the formula given:

HP = (0.8 × Factor)−25
HP = (0.8 x 56.65) -25
HP = 20.32

We see that Boston Whaler has given their boat a maximum horsepower rating for tiller steering of only 10-HP. Once again, the Boston Whaler rating is less than the federal regulations permit. This is the reason that I replied that the method used by Boston Whaler to derive their maximum horsepower ratings is unknown to me, as Boston Whaler is clearly not using the federal regulation's method.

If you use the even more restrictive federal regulation for flat-bottom hard-chine boats, the calculated maximum is still 13.3 which can be rounded up to the nearest multiple of five, thus 15-HP.

Thanks for the input guys. I am going to be searching for a pull start 15 hp short shaft engine. Hope to find the an engine like an E-TEC that burns clean. Any other engines with that type of clean burning technology out there? I am grateful for all your responses.

I have found some good buys on long shaft engines, besides the obvious that the motor is setting lower in the water. What would the other negatives be if I were to put a 15 hp 20" shaft engine on a 11' whaler that specs say a put a 15" short shaft on this hull.
The reason I am asking is I have a 17' aluminum drift boat that I was hoping to share a motor with. I had a 9.9 Suzuki High Thrust long shaft engine on it, but someone cut the lock and stole it off the boat. A short shaft will not work on the drift boat at all. Maybe I am asking for to much since they are such different hulls.
But what are the negative for the long shaft on the whaler.
Thanks to everyone for their insights, I am truly grateful.

Ten years ago I bought a 1996 11-footer without an engine. I bought a clean used 15-HP Mercury pull-start four-stroke long-shaft engine and clamped it onto the transom. I worried about the ill effects of the long shaft for a few minutes. I weigh about 200-lbs and sit in the back along with a 5-gallon fuel tank and steer with the tiller. It works great.

Generally, longer shafts are a problem. They oversteer, and of course draw more water. Half of the engine discussions on this site concerns engines being mounted too low, and the less desireable results.
If the transom takes a 15, why use a 20? Unless you have to???