93 50HP Merc Outboard Prop

[CHARGER]

Gday guys, I currently have a 50HP mercury outboard on my Quintrex 4.5M Fishabout Aluminium runabout with a pod, im not sure what the boat weighs but it feels very light for a 50HP to me.<br /><br />The prop at the moment is a 13P "not sure of diameter" with a heap of chunks and dents in it. with 3 people in the boat it is very quick to plane and revs to about 5200 22MPH or so, I want to get more top speed out of the boat and am looking at going to a 14P Prop as im told on light boats like mine the 14P will give more top speed with a sacrifice in torque ofcourse, Does this sound right, any idea what difference I can expect from the 14pitch?, my local prop guy said I could even goto a 15P for even more speed which id be interested in aswell aslong as its not gunna kill my motor.<br /><br />See attached pic may help as I dont know the weight of the boat<br /><br />Cheers for any help and advice<br />

 

[Silvertip]

Re: 93 50HP Merc Outboard Prop

Increases in pitch will decrease the engine RPM which "lugs" or strains the engine and that obviously is not recommended. Your current wide open throttle rpm should be about 5500 rpm so at 5200 your current prop is about right for that load. With one or two people on board I would guess your RPM is in the 5500 range and that's where it should be. The damage on the current prop may be limiting rpm somewhat but I would stick with what you have. If your engine was running faster than its recommended wide open throttle RPM, then I would suggest a prop with more pitch. But not with your current numbers. From the picture, engine height appears to be about right.

 

[CHARGER]

Re: 93 50HP Merc Outboard Prop

hmmm is there anyway to get more speed out of it? seems slow top end to me for a light boat as it really does jump out of the water and revout really quick, what about diameter increase or something?. <br /><br />Also when trying to turn the boat it cavitates unless I do a pretty slow smooth turn could the damaged prop do this?.<br /><br />Cheers.

 

[walleyehed]

Re: 93 50HP Merc Outboard Prop

A Damaged prop, transducer or speedwheeel mounted wrong (too close to center), and a worn prop can do the same. Triming too far for turns can cause venting, but with the engine on the pod, you could run the AV plate 2" or so above boat bottom, and the water-line will be the same on the engine.<br />Is there anything mounted on the transom within 12" of center, either side???

 

[CHARGER]

Re: 93 50HP Merc Outboard Prop

Transducer is mounted further over than 12inches from centre and other than that theres nothing else hanging down. I decided to buy the 14P because it was dirt cheap and near new so ill try it and if its no good ill just repair my 13P or get another one. with 4 people on on the weekend it hits 47KPH at 5100/5200

 

[CHARGER]

Re: 93 50HP Merc Outboard Prop

Update, I put the 14P Prop on and it worked great, at the same time I put a Stingray wing on the back and the boat is still as torquey as before plus I have gained a Higher top speed still at 5200/5300 RPM with 3 people onboard. Im not sure exactly how much faster it is as my damn fishfinder which tells me speed has decided it cant see the transducer but overall Im happy as!. <br /><br />One thing I have noticed tho is sometimes revving the motor quickly it feels like the prop spins to fast and cavitates a bit but if I increase throttle smoothly its fine. And it still wants to cavitate when turning at speed, the outboard just revs up and doesnt turn the boat.