All about propellers

J

jsimmons248

New member
I launched my new (to me) CD 22' Cruiser (2004) w/ twin 40HP Suzuki's on Saturday. Had a great time and I also have a bunch of questions.

To get started I am definitely going to add permatrims and am now thinking about changing the props from 3 blades to 4 blades with the idea of more control and faster out of the hole. I am not interested in top end speed but really need to get the bow down at as low a speed as possible to help reduce the pounding.

I did this with a 19' ski boat I owned and lowered my planing speed by 5 mph or so.

I have read lots on threads about props on the site and am now more confused than ever as to the size of props to buy! :?

Anyone have twin Suzuki 40's with 4 bladed props? If so, what size?

Any comments about what I am doing will be appreciated! :)
 
Both Trim tabs and Permatrims help to stop the pounding, and get the C Dory on plane faster. They do slightly different things, but Permatrims on the twin engines can do the same thing as trim tabs. May not be quite as efficient... However twin 40's should be plenty of power and get you right up.

At what speed and RPM do you think you are on a plane--and can you hold the boat on a plane at that RPM/speed.

A couple of questions first--what is you RPM and speed (GPS) at Wide open throttle? Do your current props have much cup in them? Are they SS or aluminum?

4 blade props give more stern lift--and we have found them especially good in the Cats. Rare that the C Dory 22 requires a 4 blade prop. Also remember that going down wind, you want to be able to to get the bow up.
 
I am not sure what the rpm/speed is to get to planing speed now except it takes too long and is too fast once it gets there!

A comfortable cruising speed, given the chop, was below planing speed in order to handle the pounding which was very pronounced at higher speeds.

I have 3 blade aluminum props on the engines now. ( I assume the standard OEM props)
 
A 22 typically will plane at very low speeds. At 10 knots ours is up on the water.
You need to know the prop's pitch and if they allow the engines to reach the recommended max rpm before you buy new ones. As I understand it going from 3 blade to 4 blade you need to reduce pitch by an inch or possibly two.
We have 13" pitch props on our Honda 40's. Your engines may require different props due to gearing, power band etc.
I have considered ditching our permatrims to reduce drag and installing Solas 4 blade props to compensate for the lost stern lift. Dunno if the theory is sound, though.
 
Before you go get new props make sure you have the boat motors trimmed up right. if you are bow down to much it will take a lot more speed to get the boat on plane.

So what is the right trim of the motors. First get on plane. Then a little at a time raise the motors up. keep raising them until you hear the motors race or the props spilling. Then trim down just a bit. Use the motor tilt switch just a second at a time. Once you are trimmed at WOT check your speed and rpm.

I know it sounds basic to many of us but I learned that it is only basic because if it was taught to us. A father in law that will remain name less was complaining that his 16 open fishing boat was not very fast and he was thinking of getting a bigger motor. He had just gotten the boat. I went out with him and we could only do about 20mph. He had the motor trimmed all the way down and was shoving the bow down. I told him to trim it up and he just looked at me with a question on his face. I reached over and trimmed the motor up as I stated above. we hit about 35 with just the two of us on board. He had owned boats years ago but did not know that they now had trim on the motors. So its only basic if you know about it.
 
Thanks for the tip on trim! I agree that it is critical to get the trim adjusted for maximum efficiency.

What I am trying to accomplish is the ability to get my CD 22 Cruiser up on plane and to maintain that plane at as slow a speed as possible. Lake Conroe is especially choppy which causes heavy pounding at the speed I need to get on a plane with my current configuration. :(

I have the permatrims on order and am now trying to figure out what 4 blade props I need to fit my twin Suziki 40 outboards. Solas has props a little under 12" diameter but with several pitch selections. In this diameter range you can have a pitch of 9, 10, or 11.

Which to choose :?: :)
 
Having the correct motor height is important and needs to be done before changing props

see

THIS APPLIES TO EVERY ENGINE AND BOAT AND IS NOT VERADO SPECIFIC

Before you start messing with props, you must get the engine height right. New props are WORTHLESS if they are not given the opportunity to do what they are designed for. And your engine height is probably not at optimum now. It is due to a little known fact about how mfr's rig: they "bury" them a little. Most mfrs rig the engine lower than optimum so they can keep themselves out of liability due to spinouts or blowouts. And raising to optimum won't cause blowouts. Forget all that stuff about using rulers and how far the hull is above/below the prop/plate. It's easy to tell if your engine height is right: with normal load (50% gas) ,get someone to take it up to cruise, trim it normal, and go back and look at the big anti vent plate above the prop on the lower end. It should be OUT of the water at speed, getting splashed is ok, but out of the flow. If it's totally dry in all seas, you're probably too high. If it's "buried" under the water, you need to raise your engine and then start testing props. A buried cavplate is like dragging a bucket on a rope behind your boat: total drag that hurts performance and puts pressure (pull) on the transom. Sorry, not an artist but a really crude pic might help:
for the full article go to
http://www.veradoclub.com/smf/index.php?topic=137.0

Ken from Prop Gods add his 2cw to the threads

He owns PropGods and the prop forum is very informative
 
Excellent information :!: I will perform the test as soon as I can.

This begs another question: How difficult is it to adjust the height of the outboards upward should they need it :?: :D
 
jsimmons248":2rlo2cv2 said:
How difficult is it to adjust the height of the outboards upward should they need it :?: :D
Click to expand...

I agree - great info and I'll definitely take a look at how mine is set up.

You might look for a recent thread posted by Roy & Dixie. They raised their Yamaha 80 just a few weeks ago. Roy figured out a clever way and it did not sound too difficult (especially if one of the "set" hole spaces can be re-used to advantage). I think he did it right in the driveway.

OTOH, removing the engine from the boat would give a good chance to properly isolate the core at the mount holes, so there is that.

Sunbeam
 
To get back to basics-before you order new props, you have to know what props you have on the boat now, and how well the boat behaves with them.

Without information--actual diameter, and pitch of the current props.
Taking the boat on on a calm day (early in the AM?) and running to see what the wide open speed is, where the best cruising speed is, and what the minimal planing speed is, you will not have baselines to work from.

Just going to 4 blade props may not give you either the most effecient or comfortable ride.

The permatrims will bring the stern up and give a lower planing speed.

First do the measurements without the Permatrims, then put them on with the current props and see where you are. Then you can have some intellegent information as to if you need different props, and what those may be. The C Dory is going to behave much differently than a 19 foot Ski boat.
 
I agree with Bob in that you might as well get good, solid baseline info with what you have, so that you can calculate your next moves. I know you said you have run the boat, but I would do it on

1) A calm day (if you have one). If there is current or wind do an out and back run and average the two. Get up to WOT and see what RPM's and speed you can make (I like Tom's helpful hints on trim). No matter what you plans are, the engines should be hitting the correct WOT RPM (I say that because I've heard of people saying, "Well, you aren't going to cruise at top speed, so don't worry about making recommended WOT RPM." That's incorrect as setting it up so that you can make WOT RPM means you are not lugging etc. at lower speeds too.

2) Figure out what props you have now (it may be stamped on the prop).

3) As Bob says, if you know you are going to add Permatrims no matter what (I added one just on the strength of the good reviews here on C-Brats), then add them and re-do the WOT test with the current props.

4) Then take that information and see which way you should move (presuming you still feel you should).

I've barely used my boat (been doing a bit of a re-fit), but I did do a WOT RPM test before I started "projectifying" and bought a different prop based on that data (I wanted a second prop anyway; now the original prop will be my spare).

Sunbeam
 
Our 2007 22' cruiser, with twin 40 hp Suzukis planes around 10 mph with Permatrims and trim tabs. I load the boat so that I don't have to use the trim tabs, and the engines are neutral. Minimum drag. If conditions require additional nose down, then I trim down with the engines, and then the tabs if more nose down authority is required. If running down wind, then the engines can be trimmed up, and tabs remain up. RPM at WOT with OEM 3 blade aluminum props is always between 5400-5800 RPM in all load conditions--in the range where it should be. I am a Permatrim believer, and would not consider running without them. Tabs too..
 
I have twin 40 Hondas with dolfins and trim tabs. I started with a Solas 3 blade aluminum 13" pitch (not sure of dia) my first season. The next year I switched to a Solas 4 blade alum 12" pitch x 10.8 dia. and ran them for 7 yrs. Then a Solas 4 blade alum 11" pitch x 11.1" dia. for 5 years. I don't have much comment on the 13" prop since I was new to boating and when I switched to the 12" it was at the beginning of my second season and I could not compare it to the `13". I did the switch because or recommendations on this site. I normally run on the heavy side. With the 12" I got about 28 mph at WOT of 5500rpm with 4.4 mpg (avg of approx 80 hrs/season, 850mi/season). I switched to 11" because when loaded with family and goods for a week (not normal, just once a season) I had WOT of 4700 rpm. With 11" I got 27 mph at WOT 6000 rpm with 4.0 mpg and I can't remember what it dropped to with family and all but it stayed above 5000rpm. Honda says WOT 5000-6000rpm and best I can tell maximum horse power is at 5500 rpm. My theory on gas mileage is that the 12" prop lugs the engine some (compared to the 11" - acceptable) giving better milage than the 11". I'm happy with my 11" but may occasionally use th 12" and get a 10% boost in mileage if I know I won't be carrying heavy loads.

Jay
 
Looks like I have a lot of work to do! I greatly appreciate all of the input I am getting as I really want to get my CD set up properly so we can enjoy her for many years.

This weekend I will get a buddy and be on the water early to perform the tests that have been recommended. I think the prior owner left the Suzuki manual in the boat so I will check that out as well as try to determine what props I currently have. I am going to install permatrims regardless but will definitely observe how deep they run in the water and adjust the engine height if necessary.

Again, my main goal is to get the boat up on plane and stay there at as low a speed as possible. My assumption is that this will help lessen the pounding I will experience on this very choppy Lake. (Lake Conroe is almost entirely bulkheaded to prevent shore erosion so the wind and boat traffic create waves that bounce off of the bulkheads and cause choppy conditions). :x
Thanks again for the input! :D
 
If it's small chop, that will help but with the 22 hull form, anything larger than about a foot will MAKE you slow down. Let us know how it goes, an interesting and informative topic!

Charlie
 
Many props have Diameter and Pitch stamped/cast on the prop hub. Manuals often just show a range of possible Diameters and Pitch so you probably will not find the one prop you have since one prop will not fit all. First number is Diameter, second is Pitch. eg. 13 x 9.
 
As you put the boat on a slow plane, with the engines trimmed down, and the bow way down--the fuel effeciency will be down from what it might be at faster speeds. I am well aware of Lake Conroe--I spent a lot of time on it in the 1957 to 1961 era when I lived in Houston, with a 13 foot cold molded Wolverine and a 25 hp Johnson.
 
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