replacing my prop, a little confused

[KRS]

The numbers on my prop are 4878122-21, and I need to find a replacement. The iboats prop sale looks like a good time, but it appears they offer many different pitches, etc. and it is a little confusing.<br /><br />Once I know what I have, I can get ideas on a replacement.<br /><br />1987 16' bowrider, 2.5Liter Mercruiser stern drive alpha one, rated at 120 HP.<br /><br />Iboats offers everything from 11" pitch to 27" pitch. Then when I click at pitch (such as 21" as I believe that the 21 in the above number means 21" pitch) there are many choices and some have different diameters.<br /><br />I would like more top end speed, but who wouldn't I get 30 mph as an absolute top speed, trimmed and running well at 4,400 WOT (manual rates that engine at 4,200-4,600 I believe).<br /><br />I don't know how this speed compares, I'm open for thoughts.

 

[waterone1@aol.com]

Re: replacing my prop, a little confused

KRS, are you sure the above number is the whole part number ? I tried doing a cross-reference for that number on mercury marine and michigan wheel websites and came up with nothing. Do you know the manufacturer of your prop ?

 

[markvictor]

Re: replacing my prop, a little confused

.KRS, PN 48-832834A45 is a 23 pitch 14" dia.<br />That's a pretty big bite, and it will probably top out at about 4200 rpm or thereabout,you may gain a couple mph..maybe..but it will be a slug out of the hole...<br />PN 48-832830A45 is a 19 pitch, that will get you up to the upper end of your RPM range at close to the same speed, but it will jump out of the hole, figuratively speaking<br />This is based on your current performance..Is your boat a tri-hull or a V-hull? When I worked for Sea-Ray, the 18 foot bow riders (with 135 HP 3.0)<br />came stock with a 23 pitch, as the 4 cyl. drive ratio is 2.0 to 1..your drive most likely is as well. that 18 footer was about a 40 or 42 mph boat.<br />If your boat is a V-hull, you may want to tune it to spec, as it seems to me that you should be a little quicker in a 16 footer.<br /> I used to keep "loaner props" in stock for people such as yourself to "try before they buy" so to speak.. I would try and find a similar situation if I were you before I spent money on a prop that may or may not do what you hope it will do...A good prop shop will have loaners, as well as a worksheet that you can fill out that they can use to optimize your performance (IF the engine is up to par.)<br />Regards,<br />markvictor

 

[KRS]

Re: replacing my prop, a little confused

Waterone: it was dark and the drive was down, I'll check it again this morning. I don't know the manufacturer, it was on the boat when I purchased it. Let me check again.<br /><br />Markvictor: It is a v-hull, 120 HP, 16 footer. Thanks for the infomation, I saw a worksheet calculator on a website, I'll try it out.

 

[ron7000]

Re: replacing my prop, a little confused

something not right,<br />120hp in a 1987 16' boat and all you get is 30 mph? Are you sure about the 30mph?

 

[whywhyzed]

Re: replacing my prop, a little confused

If your engine is turning 4,400, you DO NOT want to change props.

 

[KaGee]

Re: replacing my prop, a little confused

Asking the question in the prop forum might get you better results.

 

[KRS]

Re: replacing my prop, a little confused

Ron7000, I tracked the speed multiple passes with my GPS, so I am pretty sure about it.<br /><br />hystat, I agree, I don't want to go any higher.<br /><br />KaGee, I think you're right, I missed that forum completely.... think I'll repost there.