more prop questions

jeffro788 · 03-29-2010, 03:14 AM

Hey guys I had a slight incident this weekend and really messed up my prop. I do have a chance at a hydromotive SS 4 blade 22p at a good price, it is like a clever prop I believe. A friend of mine is running one on a 24' fountain and loves it, he said it isn't one to pull a skier with but it is a great cruiser prop and high speed. Should I go for it for about $100, or is the 22p too much?

***mikeyt*** · 03-29-2010, 03:47 AM

It wont work on your boat. A 22" pitch will have your rpms well below the recommended range of 4400-4800 at WOT and as well you will struggle to get the boat onto plane. There are numerous posts in our "Prop Talk" thread that will guide you in your search for a prop.

jeffro788 · 03-29-2010, 02:18 PM

I think I am going to go with your set up, I did find a 4 blade 20p x 14 1/8", but it says it is a 15 spline Merc outboard, but is a 15 spline. I was pretty sure they will fit, but my friend is telling me otherwise.

***z275st*** · 03-29-2010, 09:24 PM

Hi, jeffro788

Another reason you will not want a "clever style prop" is that they are designed to run with top of the blades cutting through the surface of the water. This works well on a Fountain boat because the lower unit sits higher on the transom for speed. Mariah's unit sit lower for better general boating/water-sports. In a straight poker-run your friend has a great boat, for all- around boating fun and tight turning your Mariah wins hands-down!

jeffro788 · 03-29-2010, 09:57 PM

That makes sense, he has a Bravo III, which did look a little shallower than mine. I never did really understand what the purpose of a clever is, but he did say that he can't ski behind it and really can't turn very well.
I talked to Power Boats in Hot Springs today and told them the boat will be basically 85% cruising and 15% skiing/tubing and he said the Merc Alpha 4 is a good all around 4 blade aluminum (he told me to save my money and buy aluminum for whatever reason). I really want to with the set up that Mikey T is running so I am ordering Smart Tabs Friday, which they also said will help.
The 21p 3 blade I have just drags then finally planes out and there is a looooooooot of bow rise. However when all 200 lbs of me sat in the bow it planed out very nicely, but I don't want to depend on someone sitting in the front. I ran it this past weekend and did in fact hit 52mph at 4800 rpm with 3 1/2 people (my little girl being the 1/2), but I don't think I could pull a skier especially without smart tabs.

Also meant to ask, so I can prevent another prop disaster, does it really tear up an outdrive to have the motor trimmed up past half while running?

***mikeyt*** · 03-30-2010, 12:54 AM

Running an outdrive up (lets stick with an Alpha one here) can cause overheating problems because the water pickup is running up at (or near) the surface where there is a lot of disturbance/air in the water as your boat proceeds. This affects how well the outdrive can keep the temps down. When its run down at proper trim level then the outdrive picks up much cleaner water which helps keep things cool. That said, you can run it in the surface cutting position for short periods of time at low speed while you clear obstacles/low water depth etc.

As z275st says, the 'cleaver' style prop and outdrives used on boats like Fountains are designed to run at near surface cutting positions to reduce drag under the water and the cooling systems are designed to take this into account so they dont fry the outdrives on a regular basis.

As for the prop, an aluminum will do the same job as a SS prop at a lower cost and if the water you boat in tends to chew up props (obstacles, shoals, rocks etc) you will appreciate the lower repair cost of an aluminum prop.

***indykoch*** · 03-30-2010, 01:47 AM

Running the Alpha One at a higher trim and full throttle can also damage the u-joints and gimbal bearing. They just aren't designed to be pushed that hard for long periods with much of an angle between the drive shaft and lower unit.

But I will say - I've adjusted my trim stop to the position MerCruiser states it should be "without causing damage" and it was WAY above where I could even run it without cavitating. It's a process of turning the trim stop to a point where there's xx inches of distance between the hydraulic ram mounting bolts. So I don't think I'd have any fear of damaging, since it would cavitate before actually getting to that point.

jeffro788 · 03-30-2010, 01:49 PM

Thats what I figured, the guy that I bought the boat from told me not to trim it up and have the motor running at all. I was just talking about trimming it up at idle to keep from destroying another prop on the bottom. I have only had outboards so everything makes me nervous when someone tells me be sure to do things a certain way.
I am so glad you guys are here, I would have spent alot of money by now just to go back and fix things again!

95Z212 · 03-30-2010, 10:14 PM

At low speeds (not much more over idle) you can. Where I boat, we hang out at the 'north end' its about 4-5 feet deep. As soon as I hit the no wake zone, I'm barely over idle, and my lower unit is just a hair above 'half way' down or, 'level' (left to right) on the gauge. I've had 0 problems. I just make sure the 'plate' (where a hydrofoil would bolt to) above the prop is 3-5 inch's in the water, and idle it out.

***z275st*** · 03-31-2010, 09:44 PM

Quote:

Originally Posted by indykoch

But I will say - I've adjusted my trim stop to the position MerCruiser states it should be "without causing damage" and it was WAY above where I could even run it without cavitating. It's a process of turning the trim stop to a point where there's xx inches of distance between the hydraulic ram mounting bolts. So I don't think I'd have any fear of damaging, since it would cavitate before actually getting to that point.

indykoch,
You wouldn't happen to have a link to those instructions would you?