prop problems!!!!

[swtch7]

Good afternoon!
I am new to this forum but i am in need of some help. I bought a 1996 maxum sr2 19ft bowrider last night and have just 1 problem. The prop that is currently on the motor is this 5 bladed prop, i dont have any specs on it right now but I took it out last night and realized that this is a terrible propeller for this motor. If you are idling slow and then gun it, the rpms of the motor spins up and you can hear the prop spinning fast, sounds like its cavitating. Once on plane, you have to keep the motor trim all the way down... which causes you to have a bad ride in the boat, bouncing across the water. Once I trim up the slightest bit it sounds like it starts cavatating again. Soooo my question is what propeller would be ideal for this boat? 3 blade or 4? and what pitch and all that other good stuff. Any info would be helpful and I would appreciate it. Thanks in advance. oh, and also at WOT the RPMS are right at 7000, i need a new prop.
Ernie

 

[bruceb58]

Re: prop problems!!!!

7000 RPMS!!!!!!

I hope you are kidding. If not, you are not going to have an engine worth talking about in short order when your engine swallows a valve.

 

[Dhadley]

Re: prop problems!!!!

What motor?

 

[swtch7]

Re: prop problems!!!!

sorry, i thought i posted the motor, its a 4.3l v6 merc cruiser

 

[tmh]

Re: prop problems!!!!

I'm no prop expert, but I have learned a few things here and thru trial/error. First off, as someone else said, IF you are turning 7000 rpm you have a BIG problem that needs immediate attention if it's not too late. You can not run that engine anywhere near that rpm. One of the prop guys will know, but around 5000 or below is likely the HIGH of the proper WOT range. AGAIN, check your figures, but based on what you report performance-wise, you may very well be correct that this prop is THAT far off! It's not that it is a 5-blade, 5-blades actually improve several of the areas you are having trouble with! NO, it just way underpropped. Waaaaaayyyyyyyy !!!!!!

You need to get specs from the prop I guess, or start from scratch maybe because it's not even close. Again, others will be able to be more specific once you provide some info, but a 19P 3-blade or 18P 4-blade is certainly closer to in the ballpark than what you have.

Post what your intended uses for the boat are and what performance areas are important to you (top speed, hole shot, better control, cruising efficiency, etc.) and you will get some great advice here. Do it fast because you have a very bad situation on your hands right now. One has to wonder how long the previous owner ran it with that prop? or did he just throw that one on to sell it (no test drive I presume)?

 

[swtch7]

Re: prop problems!!!!

Im not looking for anything to fast, I will be pulling wake boarders so something out of the hole and decent top end will be fine.

 

[tmh]

Re: prop problems!!!!

Well, if you read thru the forum you'll see that prop selection isn't always an exact science. many get an idea what they need then go to a prop shop that lets you try a few.

Not knowing enough details, I'd say a 19" 3-blade or 18" 4-blade may do the job, as stated earlier. Usually the 4-blade gives better hole shot (better for water sports) but reduces top end a few mph. Sounds like that is what you want maybe.

Not being aware of what you already know, it's typical (as best I know) for SS props to get a bit more performance in most areas than aluminum, but of course the SS cost a lot more! I think you'll need to try something closer to correct before you can get any useful feedback from your performance testing. Again, it depends on whether you can try a few or have to "best guess' on one and stick with it. If you do need to get it right the first time 9no trials available) then folks here can help you more if you know: Boat weight. Gear ratio, Engine Serial #, WOT range spec, normal Load (# people, gear, etc).

Check (marked on the engine) the engine for recommended WOT range for your particular engine. Say it's 4400-4800 or whatever; you'll want to prop to keep WOT in that range with your "normal" load. So test with a normal load if you can. More load will reduce WOT rpms with a given set up, lighter and you'll hit a bit higher. Many say prop twards the higher end of recommended, not sure if this is always/usually/never best, just what many here say who seem knowledgeable.