15' going from 40 to 70 HP ??

[KurtG]

I have an older 40HP Yamaha built Mariner on my boat (15' Mckee-whaler like but heavier). I've been keeping an eye out on a replacement while I'm waiting for parts for the Mariner which are difficult to get. Yesterday a relatively new 70HP 2-stroke has popped up as an option.

I prefer the weight of a 40 as I can handle it myself (i.e. threw it in the trunk to take it to the machine shop to get a broken bolt removed), and had been looking at the 50HP range, but find myself seriously considering the 70 given the year and price (haven't seen it yet).

The 40 weighs around 150 lbs and the 70 would be near 230 I understand. The boat is rated for 40-70 HP.

The deck is self bailing at 40 HP, but suspect the 70 would submerse the rear deck drains if they were removed. The boat is trailered, so this probably not a huge deal.

The boat is rated for 70 and the 40 pushes it in the mid 20s (25-27) at WOT. However, we mostly put put put.

Any comments?

 

[JB]

Re: 15' going from 40 to 70 HP ??

70HP what? Yugo?

 

[KurtG]

Re: 15' going from 40 to 70 HP ??

sorry- a 2-stroke Yamaha. It is ~5 years old.

 

[Chris1956]

Re: 15' going from 40 to 70 HP ??

Kurt, You are about to add 75% more HP to the boat. Performance will be quite different. I would look up the weight of the motor on the NADA site. 230# sounds high, since that motor is likely a 3 cylinder.

 

[KurtG]

Re: 15' going from 40 to 70 HP ??

I have 143lbs for the 40hp Mariner and 228lbs for the 70hp Yamaha. I'm pretty sure that the 70 is a 3. The weight appears to be inline with other options, but still a bit more than a 40 2-stroke.

The one I looked at the most was a new Yamaha 50 hp 2-stroke that was 189 lbs. I thought I could also find a late 90s used 48 HP Johnson/Evinrude I think they are about 185 lbs too.

yamaha 40 4-s is 183 lbs, 50 4-s is 237 lbs
e-tec 60 is 240 lbs
Suzuki 50 4-s is 243 lbs
Honda 40 4-s is 212 lbs

 

[Willyclay]

Re: 15' going from 40 to 70 HP ??

I went through a similar repowering that you are considering. I started with a 35HP Johnson on my 15ft Glastron V-153. It would run in the mid-20's and also pull an adult skier from a deep-water start with two skiis. I upgraded to a Johnson 75HP V4 that was listed at 275lbs. My speed increase was only into the low-30's but it handled my family of five much better and would pull an adult skier from a deep-water start on a single ski. My boat was rated for a maximum of 90HP. Good luck!

 

[Frank Acampora]

Re: 15' going from 40 to 70 HP ??

Kurt: Your McKee is a semi flat bottom that has a lot of displacement reserve, approximately twice that of a deep vee, when sitting or off plane. The extra engine weight will displace only about 10-11 gallons of water. On a hull like that, it would probably be only about an inch lower in the water.

I don't think engine weight will be an issue at all AND I think you will be pleasantly surprised at the performance. When properly powered, those Whaler type hulls get-up-and-go like scalded cats.

There 'aint no substitute for cubic inches.

And, on MY deep vee Glastron V 153 (rated for 90) I went from 27 MPH with a 55 to 43 MPH with a 90.

 

[KurtG]

Re: 15' going from 40 to 70 HP ??

Thanks all for the input. The explanation from Frank about the hull shape and weight helps an awful lot too. Will see where this goes today.