4 blade props on twin 5.O lx mercr.???

[crazy charlie]

Anyone have experience with 4 blade props?? My 280 regal 8500 lbs with twin 5.0 alphas cavitates as soon as I begin to trim up or turn.I am running 14 1/2x17 alum Factory .I am considering same size 4 blade but its a lot of money for a crap shoot. Charlie

 

[DJ]

Re: 4 blade props on twin 5.O lx mercr.???

charlie,<br /><br />Moving to a four balde may help. There are a few things to consider.<br /><br />1. What is your current wide open throttle rpm? Is it within the engine makers recommended range? If not, you need to adjust pitch accordingly.<br /><br />2. Four blade props do provide more bite. However, they may take a little more power to turn.<br /><br />3. Stainless steel/cupped props will bite the best. Again, you may have to make a pitch adjustment, from aluminum.

 

[L Christopher]

Re: 4 blade props on twin 5.O lx mercr.???

Charlie:<br />djohns is all over this one. I had a hole shot issue with my 3 blade OEM prop and would cavitate in hard turns on a 5.7l with alpha. I dropped 1 degee in pitch and should have gone 2 or 3. I went aluminum because of the bucks. with twin 5.0s I would dought that power to turn 4 blades would be a problem. You may be able to find a prop shop that will let you try different demo props in order to decide what works best for you.

 

[crazy charlie]

Re: 4 blade props on twin 5.O lx mercr.???

Thanks Djohns and storm.I have to stay away from ss because of stray current in our marina.I have not checked the WOT yet.because we just got the boat 1 month ago.She cruises nicely at 31-3300 rpms but it needs to be trimmed because she is a heavy cruiser and the moment I trim I can hear it begin to cavitate.I assumed my props are cupped because they are new but I will have to check.Will I need more or less pitch??? Charlie

 

[DJ]

Re: 4 blade props on twin 5.O lx mercr.???

Charlie,<br /><br />You really need to know what your wide open throttle rpm is. If you can't get there because of the cavitation, try trimming down.<br /><br />On the other hand, if your acceleration is acceptable and you are happy with your cruise rpm/speed, you may just replace the props with the same pitch and get a good quality Merc. prop. Stay away from Michigan Wheel. If you do want to go four blade, you may go down in pitch an inch or two.<br /><br />Good point about the stray current. You may be OK with SS if you keep a sharp eye on your drive zincs and maybe add a few more.<br /><br />You may also want to look into a MerCathode system.<br /><br />Does your boat have trim tabs? If so, leave the trim alone and trim the boat with those.

 

[crazy charlie]

Re: 4 blade props on twin 5.O lx mercr.???

I had not realized that my trim tabs were not working,so I topped off the resevoir the other day and its been too rough on the water to try it out.Im sure it will make a difference.I have 2 mercathode systems and i still notice my zinc fins are beginning to show a little loss.SS would be a problem I dont need.I have 2 zinc collars on my lift cyl shafts with no loss at all. charlie

 

[Wingnutt]

Re: 4 blade props on twin 5.O lx mercr.???

I was disapointed with the hole shot and planing speed of my Regal 180 Medalian with the stock 14 3/4 x 19 three blade prop. I had tried a 14x21 three blade and liked the top end but made the planing problem worse not to mention tremendous bow rise, so I tried a 4 blade. The factory rep said to a nice compromise would be a 14x20 four blade prop. What a differance! My little 4.3 can actually set you back in the seat, the bow rise is a quick up and down, planing speed dropped 5mph, and she handles like she's on rails. Top end is about the same @40mph on GPS, and I can do the "I forgot the Columbian coffie" manuver without having to trim down, she just banks and bites. At a half throttle 30mph cruise, I can drop the hammer and actually feel some decient acceleration. The only negitive that I can find (and it just may be my immgination) is that she takes just a wee bit longer to go from popping over onto plane to cruising speed. If you do decide to try a four blade give the factory reps a call. They will ask ya a bizillon questions about how you use your boat and what you are looking for performance wise. Well worth the investment.

 

[crazy charlie]

Re: 4 blade props on twin 5.O lx mercr.???

Thanks Wingnut,Thats what I was waiting to hear from someone.When you say factory rep.,I assume you mean The boat manufacturer and not the prop manu???? charlie

 

[Jdeagro]

Re: 4 blade props on twin 5.O lx mercr.???

Crazy;<br /><br />Are you using a hydrofoil? They have a tendency to lift the stern in turns, and make the boat run bow down ( stern High ).

 

[Wingnutt]

Re: 4 blade props on twin 5.O lx mercr.???

crazy charlie, <br /><br />Actually I talked to a very knowdgable Merc prop rep via many e-mails. His advice probably saved me a small fortune in different props. Visit the Merc marine web site and follow the links.

 

[crazy charlie]

Re: 4 blade props on twin 5.O lx mercr.???

Thanks again Wingnut.Nauti--I dont have any foils on the drives.It already runs with the bow down and when I trim the drives up to get the bow higher,they begin to cavitate almost immediately.Its got to be the props.I think I need a little more Bite. Charlie