Finding the perfect prop for the 3.0L

[TrailerTramp]

Hey there fellow boaters!

I've been researching for a new prop for just over a week, and I can't seem to pin-point the information that I need. I've used Mercury's "prop finder tool" and others, but none cover older outdrive gear ratios. Also, the prop that came on the boat from the factory doesn't seem right to me, and I'm concerned it may be "watering down" the outdrive's ability. Hopefully this will help others since this style of boat, the cuddy runabout, is popular on the great lakes. I'll provide as much info as possible...

1997 Citation 20.5' Cuddy (dba Sea Pro) 3.0L, 1.94 Alpha 1 w/Doel-Fins.
Boat weight including engine and max fuel weight (no passengers): 2,800.
Usage: Lake Erie (pulling tube, getting to islands, some fishing, no skiing).
Original Prop from factory: 48-78116-15 (15.25d x 15P & 11deg rake) resurfaced once.
Top Speed: 28-29mph using a Garmin Chartplotter GPS.
Climbs on plane around 18mph.
I don't have any reliable WOT info other than Merc says 4400 to 4800.

Simply put, my boat is a dog, it takes HOURS to travel 10 miles in mild rolling waters. Also, in larger swells the boat struggles to climb waves, almost plowing into them, and then it surfs down the other side. I've been caught out in some 5 to 6 foot swells that really gave me the white knuckles. Part of my problem is that my boat is probably too light and not designed for large open bodies of water. It does do much better on smaller inland lakes, but I live 1 mile from Lake Erie, so that's where I boat the most.

I would like a prop recommendation. #1, I feel the 15 pitch prop is not a good match, anyone agree? I've been considering a 3-blade stainless and aluminum, as well as, the new Alpha-4 14x20 or 14.25x18. I've read where 4-blade units can offer a secure ride, more control, and less vibration. Also, any decent increase in pitch would help my sluggishness. I'd like to be between 35 and 40 mph. That would others think?

 

[Silvertip]

Re: Finding the perfect prop for the 3.0L

You have a very wrong idea of what a pitch change does for you. Increasing pitch increases speed at the cost of hole shot. Decreasing pitch increases hole shot at the cost of top speed. Think of it as shifting the transmission in your car. 1st gear has lots of power but limited speed before the engine runs out of revs. 2nd gear makes you go faster but you don't have the power you did in 1st. As you get into overdrive the engine is loafing but there is little actual power on tap. Without any wide open throttle reading we can't be of much help. What Mercury recommends (4400 - 4800) is ideal. What you are actually experiencing determines what changes must be made. Doesn't the boat have a tach? If it does and is not working -- fix it before you spend money on a prop. Then make sure the engine is properly tuned, is making full power, and that the boat is not full of water soaked foam and the bottom is not fouled with marine growth. Then and only then consider a new prop. But in your case, a 20P prop will make matters dramatically worse. I'm guessing, but I suspect your engine is down on power or the throttle is not opening fully or it is simply "tired".

 

[steelespike]

Re: Finding the perfect prop for the 3.0L

I can't speak to much to specifics but thats a lot of boat for a 3.0
That combo may very well be a dog but we may be able to improve things.
Unfortunately your rpm at max throttle is the key to figuring where your at.
While the the fin may help you on plane it can create other problems as well.Including loss of top end.May handle awkwardly in a following sea.Smart tabs or powered tabs are a better choice. Generally a 4 blade will improve low end performance with a slight loss of top end.
A 15" pitch on that application doesn't seem extreme to me usually factory recommended props are selected leaning toward speed which ususlly sacrifices hole shot.You might check out the Turning point Hustler props.
They deliver ss performance at al prices.You might want to check that the motor is in excellent tune,throttle opening all the way,good compression.
Trim and weight distribution are critical as well.
Late at usual takes me forever to type.

 

[TrailerTramp]

Re: Finding the perfect prop for the 3.0L

Thanks for the insight. I understand the fundamentals of how the pitch of a prop works i.e. how many inches of forward travel per revolution, and I know that as you move up in pitch, the prop moves through MORE water, but has LESS grip on it. I do have a working tach, but I can't honestly remember what it was reading last summer. It'll probably be a couple weeks yet before I hit the water (we just got hit with a snow storm here in Ohio), I was just looking to get things upgraded before the season started.

I was under the impression that the WOT was a target range that you could select a prop to manipulate and achieve. Sounds like I need to establish a baseline of data first with my present prop. It's in good condition. The engine shouldn't be too tired, I've been attending classes in the summer from 2001 until last summer, so I would imagine I have around 120 hours on the engine and outdrive. I'd like to follow up on this once the weather breaks.

 

[Tail_Gunner]

Re: Finding the perfect prop for the 3.0L

Two ways to go with a boat of that size with a 3.0 Trim Tab's and a big eared 4 blade..Pontoon prop or pusher prop. Gear the prop as stated to 4800 and that is what you have to work with..maybe 35 mph..

Gearing a prop to the boat..I guess if you think of car that has one gear that drives you from 1000 rpm to 4800 rpm..That properly pitched..Then you have your bow lifter or stern lifter's....Simply said as QC stated one of those types of props will balance your hull on the water..in the stern or in the bow..the one that goes the mostest... win's...