Whaler Central - Boston Whaler Boat Information and Photos

Posted by 17whalerhelena on 07/10/19 - 10:05 AM

Hi all, I am reaching out & looking for some advice on my numbers on my boat. Here is the info below.

1989 17 Montauk
24 Gallons Fuel
1 Person- 250 lbs
2 Batteries at Stern
90 Yamaha 2 Stroke (2007)- 230 Hours- Compression 125, 122, & 120
Factory 17k Propeller (Painted Stainless)
Mounted all the way down (top hole)
Boat is bottom painted
Max Speed is 31 MPH.
Max RPM is 4700 (Factory spec is 4500-5500)
Empty, the boat floats properly

My buddy's 16 Nauset with an older 70 Yamaha comes right on past me.

The carbs were rebuilt 2 years ago & I have had (2) mechanics run the boat and tell me its running within spec.

Do you all have any suggestions?'

Thank you,

Posted by Blackduck on 07/10/19 - 2:19 PM

Two quick points. Boat should be doing 42 mph, or so. Prop is wrong, you should be running at 5500 rpm. Too much pitch. Try a different prop with less pitch and performance will improve.

Posted by Phil T on 07/10/19 - 2:52 PM

Walt is right on the RPM's but I don't think it's the prop.

Here is a list of the recommended props for the Montauk with the Yamaha 90 2-stroke that members have tested.

13" x 17" Yamaha Painted Stainless Steel
13-1/4" x 16" Yamaha Performance Series Three Blade
13-1/4" x 15" Turbo 1 4.25

Raise the engine so the top bolts are in the 3rd hole from the top.

Top
0
0
0 <---- top bolt in this hole.
0

I think that it may be the engine is not running right. Dropping a cylinder or bad powerpack?

Posted by 17whalerhelena on 07/10/19 - 3:11 PM

Blackduck wrote:
Two quick points. Boat should be doing 42 mph, or so. Prop is wrong, you should be running at 5500 rpm. Too much pitch. Try a different prop with less pitch and performance will improve.

I too agree I would like to see more RPM out of it. If I reduce pitch however (currently at 17) I will increase rpm and drop even more speed. Right?

Posted by 17whalerhelena on 07/10/19 - 3:13 PM

Phil T wrote:
Walt is right on the RPM's but I don't think it's the prop.

Here is a list of the recommended props for the Montauk with the Yamaha 90 2-stroke that members have tested.

13" x 17" Yamaha Painted Stainless Steel
13-1/4" x 16" Yamaha Performance Series Three Blade
13-1/4" x 15" Turbo 1 4.25

Raise the engine so the top bolts are in the 3rd hole from the top.

Top
0
0
0 <---- top bolt in this hole.
0

I think that it may be the engine is not running right. Dropping a cylinder or bad powerpack?

I will try changing the mounting of the outboard as you suggest. I had two mechanics run the boat and they said it is operating correctly (spec is 4500-5500)

Posted by 17whalerhelena on 07/10/19 - 5:37 PM

I did the cylinder test tonight removing each plug and listening. They all sound the same. How can I tell if it’s the power pack? My current prop is the first one you listed. If I reduce pitch I will gain rpm and lose speed. If I increase pitch I’ll lose rpm and gain speed but at 4700 rpm I don’t have any to lose at this point

Posted by Blackduck on 07/12/19 - 7:36 AM

Well yes, probably isn't just the prop. If you could gain 1 mph per 200 rpm, you would be at only 35 mph, on the optimistic end. So, either the motor is not making 90 hp ,or the boat weighs a whole lot.

Posted by biggiefl on 07/16/19 - 10:22 AM

Just like on the wave....put throttle at full and make sure you are getting 100% throttle. Very easy to mess up or have a bad cable that is limiting the range.

PS if that is good, check timing advance.

Edited by biggiefl on 07/16/19 - 10:23 AM