Wrong Prop causing problems??

[boatingfool]

1984 Bayliner, Volvo AQ125 A, Vp 270 outdrive<br /><br />Here lies my problem.<br /><br />I bought the boat at the beginning of last seasonand the guy told me he just put a new prop on but had not had the boat out since.<br /><br />Apparently there are left and right handed props. Whatever prop he put on was opposite of what was on there.<br />When I put the boat in forwards it would go in reverse. I solved that by changing over the shifting likage. Problem solved.<br /><br />The problem I still have is this:<br /><br />I have no idea what size prop is on there other than it is a 3 blade prop.<br /><br />I did not know my max rpm so I have not gone over 4500 (Well occasionaly but not for very long).<br />I found out Max rpm is 4400 - 4800.<br /><br />At 4500 rpm I am only at about 3/4 throttle or slightly less than that.<br />If my max rpm is 4800 I will break that easy if I go to WOT.<br /><br />Is my pitch to low ?? to high??<br /><br />will one of those conditions (to low, to high) cause high rpm with lower than expected speeds??<br /><br />At 3/4 throttle setting and 4500 rpm I am barely breaking 30mph with the fam on board. <br /><br />I went out with a friend on his boat yesturday afternoon and he has a 19' deep v cuddy cabin.<br /><br />Much, much heavier than my boat. He is only powerd by a 4cyl 130 hp engine against my 4cyl 125hp.<br /><br />His boat at WOT throttle hit 40mph easy at only 4100rpm.<br /><br />Having basicaly the same hp and considering I weigh more than a few pounds less He still walks away from me on the lake.<br /><br />I got kind of long winded so lets recap my situation:<br /><br />Max rpm for my engine: 4400 - 4800<br /><br />At 3/4 throttle Iam reading 4500 rpm at around 30- 35 mph depending on amount of passengers.<br /><br />Heavier boats with same power who can open their throttle all the way and not overspeed engine(unlike me) go considerably faster at lower rpm.

 

[jdcook]

Re: Wrong Prop causing problems??

boatingfool, <br />First of all I think that they make props that spin diff ways, I don't think that changing the shifting linkage would be the first thing that I would do, but if it works it works!<br />there should be a number stamped on your prop that tells you the size. There should be a series of numbers a dash then two more numbers.(merc. props) The first numbers are the part numbers. The last two numbers are the pitch of the prop. What you need is a prop with a higher pitch. For every increase in pitch, you lose 200 rpm. If your prop is a 15, then I would go to a 19, that should drop your rpms about 800, and then adjust from there. <br />Hopefully any of this helps.

 

[Boatist]

Re: Wrong Prop causing problems??

Boatingfool<br />I agree with Jd cook. Sometimes must take prop nut off and washer and will find part number or size and pitch there. If prop has been painted can be hard to see. If can find no number then may have to take prop to a prop shop and ask to tell you the pitch. you can messure the diameter yourself. I would run all the way up to your max rpms and check how much throttle left.<br />Also I would buy the standard right hand screw prop and change your linkage back. I do not know your motor or outdrive but some reverse gears cut different and not designed for long term high speed. A prop that puts you in lower half of your WOT rpms (4500) at full throttle will give you best speed and fuel mileage but you will loose some hole shot.

 

[boatingfool]

Re: Wrong Prop causing problems??

Thanks for the replies!

 

[flashback]

Re: Wrong Prop causing problems??

My friend, a prop is only efficient in the forward gear. if you have a prop that is made for a left hand rotation and your boat is a right hand rotation, then changing shift lingage or anything else will not work very well. if you think you have the wrong prop, get a basic book on how a prop works and you will see that you cannot effectively interchange the two....... if you have a single engine you most likely need a right hand prop. that is a prop with the leading edge of the blades the nearest to the transom and the prop turns in a clockwise rotation standing behind the boat. (if the shift lingage is correct)anyway good luck

 

[boatingfool]

Re: Wrong Prop causing problems??

Flashback,<br />I have consulted several mechanics recently.Some of who specialize in Volvo and all agree that the interchangeable prop(left or right) is a design volvo employs on several outdrives. Mine being one of them.The gear ratio in forward and reverse is the same.

 

[flashback]

Re: Wrong Prop causing problems??

boatingfool, your original post sounded like your prop was either left or right hand and that the one you have is opposite of what it is supposed to be..not having, or ever working on a volvo, i wouldn't know if there is a prop that works equally well in both directions. I was going on props in general... sorry if i mislead you.

 

[Doug Durako]

Re: Wrong Prop causing problems??

Pitch should be stamped on the prop---or go to Volvo and ask what was standard for that drive and year. Sounds like you need two more inches of pitch (2 inch pitch increase equals about 400 RPM decrease).<br /><br />Right handed stainless steel props are much easier to find so you might want to flip that linkage lever back over on your drive unit.<br /><br />Ebay, motors, boats, props----good place to look.

 

[giniustflord]

Re: Wrong Prop causing problems??

NO GUYS I HAVE THE SAME OUTDRIVE ANDAND IT DESINED TO BE SWICHED FROM RIGHT TO LEFT HAND PROPS WHITH NO AFECT ATS A VOLVO PENTA DESINECOURS I ONLY BUY RIGHT HAD PROPS BUT DOSENT MEAN ANYTHING DONT KNOW WHAT SIZE BOAT UOU HAVE BUT ON MY 20 FOOT BAYLINER TROPHY 1984 2O60 I USE A 13 PITCH 15 IN PROP WHEN IM LOADED IT WILL DO 48 NTO 49 HUNDRED RPM WHICH IS WERE I WHANT IT FOR MAXIMUM HORPOWER AND A 15 PITCH WHEN IM LIGHT

 

[Dunaruna]

Re: Wrong Prop causing problems??

Ginius,hit the capslock, looks like your shouting. Bootingfool, volvo designed that linkage to change rotation so that left or right props can be used, its a cheap way to have opposing screws on a dual setup. I,m no prop expert but every boating setup is different and therfore requires a little experimenting. Start with what has been suggested with more pitch to decrease rpm and go from there. Beg & borrow from mates, prop shops etc. until you have what your happy with. I use a 15 x 19 for skiing (better hole shot) and a 15 x 15 'elephant ears' to get out to my favourite fishing spot (lower cruising rpm = better fuel economy). Volvo props are easy to change so dont be afraid to have a couple if the budget allows. Aldo

 

[ahein]

Re: Wrong Prop causing problems??

Boatingfool,<br />Volvo outdrives were designed with the unique, and time-proven, feature that allows you to use either a left- or right-rotation prop simply by changing the shift linkage from one side of the cam to the other. The gear ratio remains exactly the same whether the prop shaft is spinning clockwise or counterclockwise.<br />With that being said, I would suspect that your prop is under-pitched. As a general rule, you lose about 200 rpm for every inch of increased pitch. For example, if you were running a 12-pitch prop and changed to a 16-pitch prop, you would lose about 800-900 rpm. Remember, increasing pitch also increases the theoretical distance that the prop advances in the water per revolution. Again, a 16-pitch prop would theoretically advance four more inches per revolution than the 12-pitch prop. It's not exact due to factors such as prop slippage, cavitation, etc. Increasing the distance per rev translates into increased speed. The trick is to increase the pitch as much as possible without bogging the motor or degrading the fuel efficiency beyond reasonable limits. Of course, many factors affect speed besides just the prop. The type and condition of the hull, weight of the boat, trim attitude, water and wind conditions, etc can all have dramatic effects on performance.<br />Take the advice of earlier posts and have your current prop pitch and diameter measured. Then go to Michigan Wheel to find out what you should be running. They have an interactive analysis form called Prop-It-Right that you can fill out with all your boats specifics. They will tell you what size prop (diameter and pitch) you should use to acheive your best speed and efficiency. Good Luck.