I need help!!!

ShorterU

Cadet
Joined
Jun 25, 2019
Messages
8
I am new to owning a boat & new to the forum. I need advice on my engine & stern drive. The boat I bought has a 350 engine in it & a Volvo penta sx 1.6 outdrive & a 17 1/4 x 21 prop 3 blade. The boat is a 1997 Four Winns Horizon RX. My question is at cruising speed it’s at 4000 rpm’s & that’s only at 20mph. This seems very high. With the boat loaded with 6 people it takes 4500-5000 rpm’s just to get on plane & at least 3 people have to sit in the front. Any suggestions or help would be greatly appreciated.
 

BRICH1260

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Jul 6, 2011
Messages
1,342
I think you have prop issues, the hub may be slipping, or perhaps you need a different pitch.
 

BRICH1260

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Prop slip is when the rubber donut between the splined shaft sleeve and the outer housing of the prop it self has lost its ability to stay "locked" together. The inner sleeve will spin with the driveshaft but the prop will not or will at a reduced rate. You will probably need a new prop.
 

ShorterU

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Joined
Jun 25, 2019
Messages
8
Thanks for the info! If I remove the prop is there any visible way to tell if this is damaged or should I just replace with a new hub kit & prop?
 

BRICH1260

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There is a way of testing for slip. One is to put an inline mark on the inner and outer sleeves of the hub and run it in water. If the hub is slipping the marked lines will not be in line any longer as the inner has turned but the outer did not. Another way, is by hand with the transmission in gear and see if you can rotate the prop. This is usually only useful when the hub is really bad. You might try to borrow a used prop from someone before buying new.
 

tpenfield

Moderator
Staff member
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Jul 18, 2011
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17,624
Another possibility is that the boat could be water logged and is a lot heavier than it is supposed to be. Definitely check out the prop slipping theory, but if that does not resolve the issue, start looking at the boat itself.
 

ShorterU

Cadet
Joined
Jun 25, 2019
Messages
8
Is it possible the stern drive is mismatched? The lower part was recently replaced due to a crack. It’s new now but is it possible the gear ratio is wrong? I’m not sure about all the markings on it. I as wrong about the prop size. It’s a 14 1/4 x 21.
 

GeorgeDes

Petty Officer 2nd Class
Joined
Sep 30, 2013
Messages
107
I have a 350(5.7l) on my FW 245 that is matched to a 1.6 ratio outdrive upper drive unit. The lower, however, is the 1.95 DP-SM and this boat will literally fly with that setup. I think the prop check is good advice.
 

ShorterU

Cadet
Joined
Jun 25, 2019
Messages
8
I’ll check the prop this weekend for slipping. Where can I find the lower unit gear ratio?
 

GeorgeDes

Petty Officer 2nd Class
Joined
Sep 30, 2013
Messages
107
From what I understand with the DP-SM, the overall outdrive gear ratio is only dependent on the upper unit and that the lower unit ratios are all the same. So to change the total outdrive ratio, the upper unit only gets swapped out. I don’t know for sure, but it may be the same with the SX lower units. Someone more familiar with the SX may be able to answer that.
 

ShorterU

Cadet
Joined
Jun 25, 2019
Messages
8
Ok, went out & tested it today. WOT is 38mph gps speed at 5600 rpm. No prop slip at all but the prop is a little damaged. Anymore suggestions as to getting more speed out of the boat? Prop is 14 1/4 x 21 3 blade turning point.
 

GeorgeDes

Petty Officer 2nd Class
Joined
Sep 30, 2013
Messages
107
How many people did you have on board and how long to get on plane and at what speed? Off hand, the 38 mph at WOT does not appear to be that bad but others may feel otherwise.
 

ShorterU

Cadet
Joined
Jun 25, 2019
Messages
8
Just myself onboard. Gets on plane in about 24-30 seconds. Cruising at 24mph at 3800 rpm. It’s about 23mph to plane out.
 
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