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  Propping a 15' Super Sport

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Author Topic:   Propping a 15' Super Sport
Sunseekr3 posted 09-20-2003 02:11 AM ET (US)   Profile for Sunseekr3   Send Email to Sunseekr3  
I recently purchased a 15' Super Sport with a 70 hp Yamaha motor. The lower unit and prop were stolen while the former owner had it in storage. The lower unit is almost on and I was wondering if anyone knew what diameter and pitch of prop was correct for this boat/motor combination. Also I was reading about the turbolift wing for the lower unit. Does anyone know where to get info on them and where to buy them?

Thanks

Peter posted 09-20-2003 06:37 AM ET (US)     Profile for Peter  Send Email to Peter     
I have been using a basic 13x19 aluminum Yamaha propeller on a Yamaha 70 / 15 Super Sport. The Yamaha achieves 5900 rpm at WOT and pushes the 15 to a maximum speed of around 43 mph. I don't believe that a turbo lift wing is necessary.
Bigshot posted 09-20-2003 11:46 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Go with the 19" and forgetabout a hydrofoil or equiv on a 15". If you REALLY need one, I bet anyone I know has a few laying around for free.
Sunseekr3 posted 10-06-2003 08:39 AM ET (US)     Profile for Sunseekr3  Send Email to Sunseekr3     
Thanks for your help with the propping issue. I finally got the boat in the water and running half way decently. I did have one more question though...when running at about 3500 rpm with the engine trimmed all the way in I am seeing a lot of water spraying up and forming a Vee at the transom. Is this normal for the 15' Super Sport? If not is the motor mounted too high or too low? The dealership did pull the motor off and load test it prior to reinstalling it on the boat. Any ideas about this?

Thanks

Peter posted 10-06-2003 12:53 PM ET (US)     Profile for Peter  Send Email to Peter     
With the motor trimmed all the way down, motor mounted all the way down, my 70 Yamaha makes a serious cut in the water to form a vee shaped wake with a visible cone or jet of water in the middle. I believe it is caused by the relatively large gearcase that the 70 uses. When the motor is trimmed up the wake flatens out.

Bigshot posted 10-06-2003 01:54 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Pulled the motor off and load tested it.....hahahhahaha!

Find a new mechanic.

engine should be about 1" or so above the top of the transom. If you are not mounted flat on the transom, she is OK and spray is normal when trimmed in like that, trim out till she porpoises or steering gets light, never run trimmed in like that.

Peter posted 10-06-2003 04:13 PM ET (US)     Profile for Peter  Send Email to Peter     
My motor is flat to the transom, not one inch up. Has to be that way to use the blind hole based on the original bolt pattern used for a 48 Johnson. I suspect that Sunskr's is that way too.
Sunseekr3 posted 10-06-2003 05:32 PM ET (US)     Profile for Sunseekr3  Send Email to Sunseekr3     
Thanks guys, I will try trimming the motor out farther. Hopefully I will be able to take it out on Wednesday of this week as the temp is supposed to be in the mid 70s. I'll let you know how everything works out.
Sunseekr3 posted 10-09-2003 08:06 PM ET (US)     Profile for Sunseekr3  Send Email to Sunseekr3     
The weather here in Michigan finally gave us a bit of Indian Summer and I had a chance to run the Whaler in Lake St. Clair. I tried trimming the motor out and it did help eliminate the Vspray I mentioned in an earlier message.

I do have another question though. The 70hp Yamaha still runs rough at idle through about 1400 rpm. At about 1500 rpm it smoothes out a bit but up through 4000 rpm it sounds very throaty..almost as if it is not quite up to snuff. Although it runs much better than its first time out I think it still needs some more work. If any of you folks have a 1992 or so Yamaha 70 hp motor I would welcome your opinions and comments.

Thanks in advance!

Peter posted 10-10-2003 10:17 AM ET (US)     Profile for Peter  Send Email to Peter     
Sounds like its normal. The "pulsed tuned exhaust" three cylinder Yamaha 70 works through some exhaust harmonics, one of which is very noticible at 4400 rpm. My 2003 Yamaha 70 runs a little rough up to 1500 rpm. Its fairly smooth and "throaty" up to 4400 rpm. It sounds horrible at 4400-4500 rpm, above 4500 it sings.

When I first got mine, I went through the same thought process. I thought there was something wrong with the motor and have come to realize that its normal.

Bigshot posted 10-10-2003 11:31 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Dump a can of Techron in the next tank with some super unleaded....should clean her out.
Capt_Tidy posted 10-10-2003 07:26 PM ET (US)     Profile for Capt_Tidy  Send Email to Capt_Tidy     
On my Striper with 84 Envinrude 70... I run a 13 1/4 x 19 in the ocean and love it... quess I'll have to add a tach but it a rocket. Peter's engine sounds about right... only sounds right WOT.

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