Prop Advice Needed ?

[Mike]

Hello all,

My hole shot is terrible with more than just me in the boat. My setup is a 2004 Trophy 2052 with merc 4.3l carbed / thunderbolt igniton, alpha 1 gen2 running 1.62 gears with trim tabs. The boat is heavy at approximetly 5000lbs and under powered for the altitude about 6200ft. I'm currently running a 14.5 ptich 4 blade which is just about as low of pitch as I can find in a 4 blade for my application. At WOT with this set up I"m turning about 4300 rpm which is a bit low , and reaching a top speed of about 31-32 mph.I'd like to be right up against the rev limiter at approx 4850 so when I am loaded I'm running closer to spec. With the a full tank of fuel two large dogs and one small wife It took me a country mile to plane out last weekend and really worked the motor out. I'm going to be testing some different props this week, my fear is that with a three blade in the correct pitch say a 13 or 14 ( which is what the merc prop selector returns as possibilities ) is that I'll get the rpms but with a ton of prop slip. I'm really starting to think I may need to throw some high altitude gears at this thing to get me back into more commmon prop sizes. Has anybody had a similar expeirance, if so what was yor solution? Any thoughts our comments would be appreciated!


Thanks, Mike

 

[SuperD]

Has the boat always lived its life in high altitude? Carbed motors also need to be jetted for high altitude. What diameter prop are you running?

 

[Mike]

I bought the boat out of CA and had it re-jetted prior to last years season the motor was inspected prior to purchase and described in the report as " perfect running condition". The diameter of the prop is 14''


Thanks Mike

 

[downriggeral]

First of all a couple of questions about the re-jet. They could have gone too lean by reducing the jets in the carb. Pull a couple of spark plugs and look at the color on the tips. White is Way too lean. Tan/brown about right. If they went too lean you would have a dramatic power loss and it's not good for the health of the motor.

As for the prop there are two designations. The diameter and the pitch. You gave us the diameter and not the pitch. Sounds like you are over pitched for sure. As for the four blade it too may be too much prop for the application. A three blade with the proper pitch may be the ticket. Once that is all figured out I really love a stainless three blade.

Do you have a prop shop in the area? Their knowledge will be a life saver.

Hope that helps - Alan

 

[Finatic]

Try giving Kevin Taylor at R&R PropShop in Las Vegas a call. He is a great guy who knows props and will take the time to help figure out the solution to your problem, one way or another.

http://randrpropshop.com/

 

[Mike]

Alan you are correct about the prop it is a 14.5 x 16, was going off of memory yesterday at work ( which apparently isn't that good). The plugs looked great this spring when I changed them, a nice tanish brown. The local marina will let me try whatever prop I want so I think I'll head down Tuesday and try every prop in the shop until I get the best results. Fin thanks for the info if I can't find a prop locally I will definitely give them a call. The boat had an old beat up aluminum 16 pitch 3 blade on it when I bought the boat. The four blade was suggested by a local mechanic. After doing some research I would think to be right the pitch should have been dropped a few inches on the four blade, and by doing so would still have been the close equivalent to the 3 blade 16. With the boat coming from sea level with a 16 pitch on it I'm thinking that 14 possibly a 13 might get me where I need to be.

Thanks for all the responses !

Mike

 

[jopes]

that is a fairly heavy boat for a 4.3L. If my memory is right merc says the best props for their stern drives is the 19 and 21 pitch and they power / gear the boats to run those choices.

With the elevation loss, That 190hp 4.3 is loosing ~ 35 hp @6200 feet. So that gives you about 155 hp to play with. Pretty low numbers for a heavy boat.

What kind of trim tabs are you running?

Some options come to mind, are a different gear ratio for the lower unit, or a higher HP 4.3 from US engines. Neither are cheap. The engine with about 50 more HP will run you $2400 just for the engine.

 

[jopes]

This is probably one of the best prop guides I have seen so far.

http://boatpropellers.iboats.com/propeller-tutorials/rpm/?cart_id=362775623

 

[Mike]

I have a feeling doing a gear swap would be about the same price as a new drive from SEI. I'm running lenco 9 x 12 trim tabs I've thought about adding more length like 9x 24 even though you get more advantage from wider chord. I guess I won't know where I'm at until I exhaust all my options for props.

Thank you for your response

Mike

 

[jopes]

SEI is a great choice.

I'd try the 13 or 14" pitch 4 blades you have talked about if they have them. You will get on plane better but your probably going to loose a few mph top speed.