sylvan 21 w/115 yam size prop?

[gutts1]

Hello
Thank You all for the help .
Long story/short version , new used-sylvan 21'cuddy cabin 1984 i.d. #syl00335m84b
33mph+/- @ 5300rpm motor sounds like it is working hard
boat seems to take a long time to get on plane.
Motor is all the way down on transom


I think the prop [ 13 1/2x17-k ] is spun [we all know the sound]
question about a new prop--- less pitch = less speed more rpm less stress on motor?
Any advice on this subject would be helpful .
WHAT SIZE WOULD BE BEST ??
Does anyone out there own one of these boats ?
I have never seen one before .

 

[BaileysBoat]

Re: sylvan 21 w/115 yam size prop?

I looked at these a few years ago, nice boat. Most of them seemed to have a 3.0 mercruiser, about 130 hp. I always thought 150 hp would be better. These are light for the size but high windage. From the numbers I would start with a 15p.

 

[gutts1]

Re: sylvan 21 w/115 yam size prop?

Thank You
Yes That Makes sense . It seems at wot that the motor is working to hard .
When it is there the mechanic in me wants to slowly back off til i hear the motor "coast" , or relax a little , but , i suppose that does not happen on the water....
Any thoughts on the height of the motor ? It is down right now .

 

[BaileysBoat]

Re: sylvan 21 w/115 yam size prop?

Your boat is not a deep v, it's just about flat at the transom as I recollect. As a reference point the cavitation plate should be level with the bottom of the transom.

 

[steelespike]

Re: sylvan 21 w/115 yam size prop?

Hello
Thank You all for the help .
Long story/short version , new used-sylvan 21'cuddy cabin 1984 i.d. #syl00335m84b
33mph+/- @ 5300rpm motor sounds like it is working hard
boat seems to take a long time to get on plane.
Motor is all the way down on transom


I think the prop [ 13 1/2x17-k ] is spun [we all know the sound]
question about a new prop--- less pitch = less speed more rpm less stress on motor?
Any advice on this subject would be helpful .
WHAT SIZE WOULD BE BEST ??
Does anyone out there own one of these boats ?
I have never seen one before .

Gotta get for sure prop size.What load are specs from?
A true spun hub you don't go anywhere.When a hub spins it goes from working to non working pretty much no middle ground.
Thats a lot of boat for a 115 so hole shot may be a little slow.
33mph is pretty good if its gps otherwise who knows?
My info indicates the 2 stroker V4 115 is rated at 5,000 and I would guess it could be run at 5,500.So your not really over propped except from a hole shot standpoint.Yes you could shoot for that 5,500.A 15 would put you at about 5,700.it would give you a little whole more hole shot.Antivent plate even with the bottom of the boat is considered a starting point.If you have no ventilation the motor is too low.
If you can raise the motor you could gain a couple of mph and some rpm
perhaps a slight improvement in hole shot.
Something like smart tabs might be better than a prop change.They would get you your hole shot,more stable ride,stay on plane at lower power,less wander at no wake speed.and they are said to deliver more speed.Excellent factory support.

 

[gutts1]

Re: sylvan 21 w/115 yam size prop?

AHH
The wonderful world of "boat tuning"
I borrowed a 15 from a friend , will try that the next time out . New England , the boat days are soon coming to an end . A few more trips out and that will be it .


I was wondering if what i was hearing was cavatation instead of the prop spining ? I did Have the trim up a bit ..... No there were the teltale circular marks on the ends.......
Thank You

 

[steelespike]

Re: sylvan 21 w/115 yam size prop?

Technicaly your refering to ventilation; cavitation is a different animal.
You could be have a little venting but usually once it starts if you contnue to accelerate it will get worse.Speed and rpm seem normal to me so venting
doesn't seem likely.

 

[gutts1]

Re: sylvan 21 w/115 yam size prop?

Hello
Back from a great day on long island sound .
When i heard the "venting" I , at once , backed it right down . Then went back to it a with a little less throttle . The different size prop is great , i do not think i lost any top , but out of the hole is much better .

Thank You All