Propeller Talk

[cbadmin]

From: LesLampman (Original Message) Sent: 11/13/2002 6:09 AM

We'll use this forum to discuss propeller selection, function, design or whatever other things come up relative to props.

Right from the beginning we need to acknowledge that while prop design is based on scientific principles; prop selection is based on some science, some math, some intuition, some experience and lots of magic. The main problem is that there are so many variables in the selection process that it makes reducing the selection process to a simple 'pick-n-go' affair virtually impossible.

Variables? What variables? How 'bout:

- basic hull design

- boat weight

- boat balance

- estimated crusing speed

- pounds/sqaure foot on planing area

- pounds/horsepower for the boat

- torque curve of engine

- acceptable wide open throttle (WOT) range

- operator performance preference

- intended use of the boat

- typical operating conditions (waves and weather)

- typical operating altitude

So, post you questions and your experiences and selection thoughts and we'll build a knowledge base here.

Les

From: Fun Patrol Sent: 11/24/2002 7:44 AM
Prop for 22 Cruiser with Suzuki 70

This is the combination I am running and, as the question comes up fairly often, here's what I have found in my real-life tests:

I run with the boat loaded fairly heavy most of the time. It saves the agonizing decision making....just take it all! For a several-day trip....full 20 gal fresh water (if a salt water trip), full 36 gals fuel, 70 lb Honda 8 kicker, 2 packed ice chests, 1 cook/advisor and 2 cats..(with litter). All this gives performance figures quite a bit less impressive than a bare hull.

My particular motor is an Evinrude 70, which is a Suzuki with a decal. The props for this application will be either 13 3/4 or 14 inch diameter. For 3,000 ft or up to about 5,000 ft I have to use a 13 inch pitch. If I want to go higher, like Lake Tahoe, I will need a bigger motor or lighter load. My 14 inch is good for all around, fully loaded up to 3,000 ft. The 15 inch works fine at sea level if not loaded to the max. I also have a 17 composite for a spare. It will move the boat, but forget a plane.

The 14 inch is not a standard size. I had a dinged 13 repaired and repitched for about $65.

Happy "testing"....Roy

From: Mike Sent: 11/24/2002 8:00 PM
Les, or anyone -

I need a prop recommendation. The highest RPM my BF75 Honda ('00) has ever seen is 5400, and that was just once and running light. I have had some bad luck with props, and I want to get it right for next season. It seems I either have my boat loaded a bit heavier than most, or my Honda is a dog, because it just doesn't want to spin up. I have checked the throttle mechanism, and it is opening fully. In the table below is the info on the props I have tried.


Prop Size


Manufacturer


RPM at WOT


Comments
3 x 13.75 x 17 Honda (Solas) 4900 Came with the boat
3 x 13.5 x 15 Honda (Solas) 5300 Bad hub, short lived trial. Had prop balanced, went haywire again - prop junked
3 x 13.75 x 15 Propco 5100 Poor manufacturer workmanship. Had to machine hub base to fit motor. Don't trust it.
3 x 13.75 x 15 Michigan 5000 Currently in use. Best of the bunch so far.

I am thinking maybe I need to go to a smaller pitch than the 15" that is normal for the Honda 75. Les, you have said before that running a four blade is similar to a 3 blade with 1" more pitch. Would you suggest trying a Solas 4 blade, 13" pitch? Aren't there some advantages to the 4-blade that make it a good fit for the CD hull?

The Honda 3 x 13.5 x 15 worked within the acceptable RPM range, but something went bad in the hub and it lost balance. Instead of taking the new prop back to the dealer, I had it balanced at a local shop and tried it again. It worked for a short while, and then went out of balance again. (Dumb not to take it back in the first place, I ended up eating the cost of the thing. The prop shop did knock his charge for the balancing off the price of the new Michigan Wheel.)

So, what do you think? Try a Solas branded 3 x 13.5 x 15? Or a Solas 4 x ?? x 13?

Thank you,

Mike

PS - Anybody want to buy some used props?

From: Fun Patrol Sent: 11/25/2002 6:29 AM
Mike:

Your situation is much the same as mine although you didn't mention the load and altitude. Sounds like you need to drop her down a gear, maybe to a 14 pitch. You might even want to carry a 13 for a spare and for higher altitude.

Roy

From: Mike Sent: 11/25/2002 4:16 PM
Roy -

Sorry, I never give any thought to altitude, because I am always at or near sea level depending on the tides. Maybe next summer if we head up to Lake Chelan I will have to think about it.

As for load, I guess I usually run relatively heavy. Full 20 gal. water tank, 48 gal. gas when full, lots of fishing gear, ice, and supplies. I also have a hundred pounds or so of gadgets (windlass, washdown pump, and a few other gizmos I have to have). I've noticed that one extra person on board makes a noticable difference in performance through the entire speed range. Two people is normal, often three or four.

To tell you the truth, I am kind of hoping somebody is pretty sure the 4-blade 13" pitch is a good choice. I recall reading some positive comments about the 4-blade, and I am sure Les has commented about the 1" greater pitch equivalency. That would make the off-the-shelf 4 blade 13" about the same as the oddball 3 blade 14" it looks like I need. I think that came out right.

The only time I have really liked the 17" pitch was running down the Columbia from Bonneville with the outgoing tide. Zipped right along, we did. Another thing I noticed about the smaller pitch props was the ability to set the idle down to about 850 rpm for trolling with the main motor. In the river current, the kicker doesn't get much use. There seems to be quite a difference in speed with just a couple hundred rpm when trolling.

Still learning.....

Mike

From: LesLampman Sent: 12/1/2002 5:11 PM
Hi Mike,

I'm coming way late to this thread ... sorry .

Generally, I've been using the Solas (Honda supplied) 4-bladed 15" pitch prop on the BF75; I also like the Solas 3-bladed 15 prop. The old Merc props worked well in 3x15 as well.

There isn't any reason to get your BF75 stirred up beyond the 5400 rpm or so it will turn now; especially if you're loaded the way you normally run. The peak torque on the BF75 is 4000 rpm and it really likes 3800 to 4200 on the CD22 (water conditions allowing). The BF90 on the same block, is a different animal; it's peak torque is up at 4500 rpm and if it can't spin up into the high 5's it isn't happy but the BF75 has a flatter and lower torque curve and pulls better in the cruising range (I'm splitting hairs here since in reality they both work really well).

I'd put a 4x15 (I leave the diamter out since we can't dictate what it is) 4-bladed Solas on there as an alternative. That will drop your rpm to around 5200 but at normal load that is still quite acceptable. If you go to the 13 pitch prop it will feel like you're stuck in 2nd gear. The advantages of the 4-bladed prop are better lift from the prop, better hole shot, more blade area for better engine loading, reduced ventilation and because of the much smaller openings between the blades it's much harder to pick up debris in the prop; and finally, the prop runs smoother. In the real world I usually choose the 4-bladed prop because of its smoothness and because it does seem to avoid dings and debris better. The other characteristics are awfully hard to quantify.

Les

From: LesLampman Sent: 12/1/2002 5:15 PM
Roy,

Great info on your Evinrude/Suzuki 70! Thanks!

Les

From: Mike Sent: 12/1/2002 6:01 PM
Les -

Thanks for your help. I think maybe I'll go to the Solas branded 3 x 15 to start with (Solas to get the serviceable hub). The max RPM I get now is 5000, with the Merc prop. The 5400 was made with the short-lived Honda 3 x 15. Except for the hub, the two (Solas and Honda) are the same configuration, right?

I understand what you mean by "stuck in second gear", but I am concerned the 4 x 15 will cut the WOT even more. For some reason my motor has a sweet spot at 4250, +/- a few. You can feel and hear the difference when you hit it, regardless of the props I have tried. Per your advice, I try to keep my cruise rpm about 1000 less than WOT, but I have been cheating a little down to around 750 less to hit the smoothest running. Especially since adding the trim tabs, the sweet spot is sweet, indeed.

The 3 x 15 should do the trick, then? If there is one available at the Seattle Boat Show, I'll probably let my wife buy it for me as an anniversary gift. I am so sweet, too.

Mike

From: LesLampman Sent: 12/1/2002 6:08 PM
Hi Mike,

The Honda props are Solas props with the fixed hubs rather than the interchangable hubs of the Solas branded props. C-Salt had the 3x15 and it worked out really well. It's also the prop I've used on most CD2 installs but my friend Mike Kurtz who has Wigeon (CD22 with BF75) really liked the 4x15 and he stayed with that. All of our CD22s have the Honda SST hydrofoil installed and that is another variable in the game of "prop the boat".

Les

From: CatmanToo22 Sent: 12/8/2002 11:09 PM
My little critter runs about 2,000 RPM under WOT. I get 6,010 RPM, and cruise at 4,000 to 4,500.

From: Molly Brown Sent: 3/17/2003 3:00 AM
Sent you an email about my performance issue with my TomCat. What size props allow you that kind of response??? Molly Brown

From: C-Worthy Sent: 6/23/2003 5:34 PM
Does anybody know what props work best on twin Honda 45s? I've got a CD 22 Cruiser and usually run it at 4500 with two souls and a husky-shephard mix aboard.
I've got 32-50 gallons of fuel and @ full water tank so I guess I'm not superlight.

Also, I've only heard the negatives of stainless props. Are their any positives other than you can reshape and file them out if you ding 'em?