Whaler Central - Boston Whaler Boat Information and Photos

Posted by REM1319 on 11/21/08 - 8:23 AM

Just got a 1987 Sport 15 Center Console with a 70 HP Yamaha and based on the wonderful knowledge from this site and others I am in the process of updating some items (pictures to follow).

Boat Currently has a Yamaha K-21 stainless steel propeller which I suspect the prior owner had on for top end when out alone and flying light.

Currently maximum RPM is 4800 to 5000 with that set up with our typical load - myself and two kids (unfortunately no speed data yet). Boat seems to "lug" and is slow to pick up out of the hole.

Boat now has Hydrodynamics 6" jack plate, new BayStar steering and I anticipate raising motor 3" to 4".

I would appreciate input on propellers.

I am thinking of the Yamaha K-19 as a start. I have heard the Mercury Quicksilver 48661384A4 19P (13.5 x 19) might be a good candidate. I also seek information of the Yamaha Performance propellers.

Furthermore, since the motor will be raised, does this variable point to a different family of propellers? I also seek guidance on possible Stiletto products as I heard Yamaha OEM and Stiletto are the same family. Is there a Stiletto prop equivalent to the Yamaha Performance family of props that work well with the engine raised almost 4"?

Top end is not the primary concern - all around performance is more important. The boat will be used for tubing, fishing, etc., with the wife and two smaller children. I would definitely would like better hole shot as my little four year old boy's favorite saying is "hit it!"

As always, your valuable insight and experience is greatly appreciated!

Best,

Greg:)

Edited by Tom W Clark on 11/22/08 - 11:04 AM

Posted by Tom W Clark on 11/21/08 - 9:46 AM

Greg,

You don't say what Yamaha 70 you have but I am going to assume you have a two stroke Yamaha 70 HP of the same vintage as the boat. If that is the case, I *think* you WOT range tops out at 5500 RPM. If you can only hit 5000 RMP, then you definitely want to reduce pitch.

You could try the Yamaha painted stainless steel propeller in the 19" pitch or the Performance Series, which is the same as a Stiletto Advantage. Yamaha owns Precision Propeller Inc., the makers of the Stiletto and Turbo brands of propellers.

The Quicksilver propeller you site above is an obsolete propeller which has been superseded by the Mercury Vengeance (a.k.a. Quicksilver Silverado). The 13" x 18" would be the size to try in this model.

Now, if you are going to raise the motor, go ahead and do that FIRST. Record your speed and RPM data and *then* make a decision about whether or not you need to try a new propeller.

Edited by Tom W Clark on 11/21/08 - 9:48 AM

Posted by REM1319 on 11/21/08 - 10:12 AM

Dear Tom:
Wow!
That was fast.
Thank you for the info.
You are correct the Yamaha 70 is 1987 vintage.
As advised I will raise the motor in the spring and test for RPM and speed.
Given the Yamaha Performance and Stiletto Advantage are siblings if not identical what models do you recommend in the Stiletto family based on your experience and the fact the Yamaha will be running on a jack plate probably 3 or 4" up.
I will also let my 4 year old co-pilot Thomas know that Tom the propeller expert is helping dad make the boat go faster when he says "hit it"
Best Regards,
Greg

Posted by ritzyrags on 11/22/08 - 3:28 PM

On that subject,
And not wanting to barge in here..
I have a 150 Merc Offshore 97 on the transom of my Classic 19'4" Outrage presently.
Upon adopting her she did not come equipped with a prop so to speak.
I have since then bought a four bladed stainless with a 21P.
Could have gone to a 19 for quicker pick up but opted for the 21 being a bit slower at start but with a bit more on the top end.
What is typically run on these unit as an average?
I am talking with the hull and outboard combination?

Serge.

Posted by theo on 12/01/08 - 5:03 PM

I have to ask why I can barely swing 15" of pitch on my '86 15' CC with a 1995 60 Merc 2 stroke and CMC 5" jack plate . I just barely touch 5300 and 41 mph with me and my windbreaker and a few gallons of gas.

I wouldn't have thought an older Yammie 70 would have enough more torque to swing 4 more inches of pitch. I'm even thinking of dropping to 13" because I feel like a 4 year old when I drive my boat and I too love "Hit it" more than any other boating term in existence!

I admittedly don't know much about it. Wonder if my hull is waterlogged?

Posted by Tom W Clark on 12/02/08 - 8:36 AM

Different outboards use different gear ratios. That is most of the difference. The 1995 Mercury 60 uses a 1.64:1 gear ratio. The Yamaha 70 uses a 2.33:1 gear ratio.

There is much more to a propeller than just its pitch. That is also part of the difference.

You have a 60 HP outboard. Greg has a 70 HP outboard. That the last part of the difference.

Edited by Tom W Clark on 12/02/08 - 8:42 AM

Posted by zotcha on 04/22/09 - 7:19 PM

#11

Greg, congradulations! You are becoming educated and working with a professional who has the best prices available on the internet. Don't be afraid to ask questions...he is a gentleman and a scholar. I know. Getting ready to rig my second 15 with a four stroke 60, just totally different applications! Good, safe boating season. zot.