Propeller Pitch

[El and Bill]

Might be good to put our collective ideas regarding prop pitch on one thread to summarize ideas for those who are buying boats.

There are a number of variables, such as the use of boat (pulling skiers would be different than fishing and both different than a 'heavy' boat of long-distance cruisers), altitude can make a difference (we knew a boater who carried a big box of props and changed them for every thousand feet of elevation change [he lived in Wyoming]), size (and number) of engines can be a variable, fresh water vs. salt water might be a variable, etc.

Size of prop might also be a factor, and how important is pitch with prop size? Should big props have a different pitch than small, all other variables being equal?

How important is pitch? Is it only at the extreme edge of variables that it is important? How much extra load does it REALLY put on an engine (how about real numbers, not just opinion). How much difference IS there in performance -- is it just a couple miles per hour at the top range and insignificant at lower speeds? (real numbers, guys, not just opinions!).

Should we carry extra props with different pitch and change them when conditions change, or is that not necessary (if pitch isn't really that important under 'normal' conditions.

So -- (if pitch is important), is it possible to summarize the best pitch for our various C-Dory types for each different variable. Or, as long as our use of boat stays much the same, should we get a prop with one size, one pitch, and live happily ever after ... ?

[dogon dory]

Sorry, Folks - Post Deleted By Author

[Larry H]

One thing that remains constant is that the motor should run in the maximum rpm range ie: 5,000 to 6,000 (this is an example, look in your owners manual for your motors max rpm range) when the throttle is wide open. If you cannot achieve the minimum rpm of the range, then your prop has too much pitch. If your motor revs above that range, then the pitch of your prop is too low.

So, load your boat with your normal load, take it out on flat water and test. Compare your rpm to the range specified in your owners manual. This give you a basis to choose another prop. If you can borrow some props for testing, that is great. If you only have one prop, test and record, then decide if you want to get another prop.

Talk to your dealer about your results and which prop to try next. Sometimes they will let you exchange a prop for another pitch if there is no visible damage to the prop.

To guestimate pitch, one inch of pitch change should result in 200-400 rpm change on WOT(wide open throttle).

As always, your results may vary.

If you take your boat to higher altitudes, you may want to have a prop with one or two inches less pitch. Motors loose 3% of HP for each 1,000 ft of altitude.

Owners of twins may want to have a lower pitch prop available for operating on one motor.

Dogon Dan is right about this topic having so many variables that it is nigh impossible to compare different boats, motors, and props.

'Propping out' a boat is an experimental process.

[dogon dory]

Sorry, Folks - Post Deleted By Author

[TyBoo]

[C-WEED]

Another unknown variable is the actual H.P. output of the engine. I have read where from the factory a plus or minus 10% variation in H.P. output from what is on the engine cover is acceptable. From the low side to the high side would yield very different results.

[dogon dory]

Sorry, Folks - Post Deleted By Author

[Larry H]

Dogon Dan,

Yeah, there is a lot more to it than just the pitch. My comments were for an owner that has a prop on the boat and is wondering if its right.

If you have a stock aluminium prop and replace it with the same model, different pitch, the diameter may be the same or slightly different, but there is usually no choice to the buyer.

[TyBoo]

[Sawdust]

Mike, Ol' bud --

Some horses are gonna go just so fast, no matter what kind of saddle you put on them. Man. a cruise of 14-15 knots, up on easy plane, is way cool. At your weight (well, the boats total weight) about 200 hp would be ideal. Pair of 90 E-Tec jewels mebbe??

Be HAPPY,

Dusty

[jlynch]

Everything You Need to Know About Propellers.

Check out this site at Mercury Marine, if you have time to read it
and can inhale all the technical information, then you can answer any
questions about propellers.

www.mercurymarine.com/everything_you_need_to_know_about_propellers5

[Redƒox]

Sorry folks fer not havin the time to read all the prior-post here consider:

Why in tarnation would you want to spin a prop faster in the water, to achieve the same hull-speed as a lower-geared outboard. There's energy wastin there.... not matter what formula is applied the way of the future is obviously to spin a steeper pitch (slower turning) and gain "traction in the water toboot Suzuki has a good explanation for this on there website (I think...if they still do)

Sorry bout the "quicky-message" and not payin attention to all that hi-tech discussin up there, but it's high-time the RedFox went fishin

[dogon dory]

Sorry, Folks - Post Deleted By Author

[Sea Wolf]

Hmmmmmmmmm.......Fun to read all the technical information over and over again and do the calculations too, but what it all comes down to is trying out props on the boat under conditions you usually operate in with the boat loaded as you usually do.

As far as the CD-22 is concerned, about a 14-17 inch pitch range with a 13 to 13 5/8 or so diameter seems to be the agreed upon common ground unless you have a Suzuki 90 with a 2.60:1 gear ratio where a 19 inch pitch may be within range.

Due to the nature of the CD hulls, we don't need high tech or exotic propellers such as the Raker, Stilletto, Rapture, or the ever popular Screaming Screw. Some of us do like the lesser vibration and better anti-ventilation characteristics of the 4-bladed props, and find they work very well.

I currently have 15 and 17 inch pitch Yamaha 3-blade OEM props, 4-blade Comprops of 15 and 17 inch pitch, and a 15 inch pitch Solas 4-blade prop. I'll let you know how they work out if I can ever get around to trying them all out!

Even part of the propeller selection process is subjective, so numbers don't always mean everything. Still helps to understand all the theory when trying to find the best fit, however. Joe.

[Redƒox]