Great Day! (Honda props)

[Mikebe]

It's been too windy, but it's looking good for after work today...

[Mikebe]

Ok I tested the Solas 4 x 11.8 x 9 pitch today. It fit perfectly with the same hardware as the OEM Honda prop. Couldn't get above about 13 knots before the prop started grabbing air. I'm pretty sure this is what was happening, because at just below that speed I can cause it to happen by going into a turn. Also, from a dead stop I can go WOT and everything is fine (no cavitation, ventilation, slippage or any thing else) until the boat gets up to about 13 knots. This seemed odd to me, because the prop was the same diameter as the Honda OEM and in my earlier test with the Honda prop I had not had this problem. So I went back to the dock and put the Honda OEM prop 3 x 11.75 x 10 pitch on and went back out for a re-test. I got the same results with the Honda prop as I did with the Solas prop, when I hit 13 knots it started grabbing air. In my previous test with the Honda prop I had made it up to 16 knots without having this problem. The only way I can explain this is that the weight and/or distribution of the weight has changed since I did the earlier test. Actually I'm sure it has, since I refilled a 6 gal water container and a 6 gal fuel tank. Also I was able to cause the problem with the Honda prop by turning (same as the Solas prop.) So, my conclusion is that either my motor is not mounted low enough, or 12 knots is about all I can realistically expect with the Honda BF50 and weight on my boat.

Edit: Both tests were without ballast...

[PeteC]

Something must be wrong because others (self included) get better performance out of the Honda 50 with either of the props you mentioned.

I have the 3-blade and get 16+ mph (14 knots) unbalasted but with a lot of stuff onboard. I have never had a problem with cavitaton that I know of.

[Frank C]

Sounds as if Mike & Pete should compare mounting of their outboards.

• Are both boats floating true to the bootstripe?
  AFt weights similar (fuel & crew)?
  Particularly bow-heavy for any reasons?
  Ballast empty.
  How deep are the anti-ventilation plates, below hull bottom?
  Do you both have wedge plates?
  Are you both trimmed fully down?

[argonaut]

Identical problem i think...
97X, honda 50HP, Solas 4x11.8x9, prop just becomes a blender at some speed, maybe 11-12mph.
No wedge.

[Mikebe]

I'm not sure what the wedge is. I'll measure my mounting this weekend. Also I had the six gallons of water, situated in the bow this time, so I had more weight in the bow this time. I'll have time this weekend to experiment and see if I can re-create the conditions that allowed me to hit 16 knots last week.

My boat definitely floats bow down WITH ballast. I don't know how it floats without ballast, since I always have ballast in when I dock. I'll check that too.

I run fully trimed down. Experimented with trimming up when having the problem, but it just made it worse.

[Robert]

If you are sucking air at the top of the prop there are two ways to fix it, more cupping of the prop or lower the motor mount on the boat.

[Mikebe]

Thanks Robert. I figured lowering the motor...but how does more cupping help?

[argonaut]

Last weekend at 4000rpm,Honda 50hp, Solas 11.8x9, with no ballast except me and mate I was making 10-11 mph... which "don't quite sound right to me".
Maybe I need cupping too. And if that doesn't work I'll have it done to the prop.

[Catigale]

Cupping will hurt your performance on a beam reach around the lake....

[Mikebe]

Last weekend I borrowed a float and decided to re-install the Michigan Wheel 4x12x10 prop. This time I paid attention to how well the prop fits into the housing with the thrust washer. It fit just fine (unless you have the thrust washer backwards, which I may have during an earlier test). The gear teeth inside the thrust washer are beveled on one end, and this is the side of the washer that should be facing forward when installed.

Yesterday I had the chance to test. Since at least two of my other props seemed to be grabbing air during my last test, and the only thing I could think of that had changed was weight/weight distribution, I emptied the six gallons of water I had stored in bow of the boat. I went out, emptied the ballast, and opened her up...13.6 knots, no ventilating, no cavitating, WOT, no problem.

I wasn't able to try the other props again yesterday, but at this point I would be willing to bet that I would not have the ventilating/cavitating issue with them, either. I will verify this at the first opportunity. Before I remove the MW though, I will put the six gals of water back in the bow and see if this causes the ventilation issue.

[Terry]

Thanks Robert. I figured lowering the motor...but how does more cupping help?

A quote from a propeller site:
"Cupped propellers have an extra curve on the trailing edge of their blades, which enables the prop to cut through water better. A properly cupped propeller should give your boat a higher top speed or allow you to go faster at the same rpm's. A rough rule of thumb for cupping says that a medium cup equals 2" of pitch. In other words, a 14" x 17" un-cupped prop could be replaced with a 14" x 15" cupped propeller and produce the same engine performance with higher speed."
Cup
"Small radius of curvature located on the trailing edge of the blade. This curved lip on the propeller allows it to get a better bite on the water. This results in reduced ventilation, slipping, and allows for a better hole shot in many cases."
Some folks are using the Solas Amita 4 X 11.8 X 9 which is not cupped. The Solas Alcup of the same size has medium cupping and gives better performance while helping to eliminate ventilation by gripping the water with the cupped edge. Cupping helps the prop get a better bite/grip on the water.

[beene]

Hi

Here is my Cupped prop....



G

[Mikebe]

Ok, I put the six gals water back in the bow, emptied ballast, and made another WOT run with the 4 x 12 x 10 Michigan Wheel. No probem, 13.5 knots. I must have had the thrust washer backwards when I had problems with it in earlier testing. At this point, I can't seem to make it cavitate, ventilate, or otherwise screw up (at WOT and empy ballast). Which means (at least to me) it's the best all around prop I have tested.

The MW is 12 in diameter and 10 pitch (and more dog-eared)
Vs the Solas 4 x 11.8 x 9 pitch.

The Honda OEM 3 x 11.75 x 10 prop gives the best top speed (about 16 knots) but only with limited weight in the boat.

Both the Solas 4 blade (not the Alcup model) and the Honda OEM would begin to cavitate or ventilate (not sure which, but I'm guessing cavitate) at about 80% throttle (about 11 or 12 knots) with the same weight that the MW handled OK. I'm sure there is a point (probably only a few pounds more) at which the MW prop would begin to have the same problem.

I think they are all good props for an M with the 50HP Honda, although as Terry and others have pointed out, more cupping would probably be better. If I were buying the Solas again I would probably go with the Alcup.

IMO the bottom line is this, the Honda 50 is only going to get your M halfway out of the hole, and in that situation, the weight in the boat and how it is distributed seems to be the biggest factor. In the end I have concluded the same as others on this board. The biggest, most dog-eared prop you can find seems to be the best overall prop (unless your boat is pretty much empty, then the Honda would give a couple of extra knots top speed).

Note: I also have an ablative bottom paint on my hull, which I'm sure also affects my speed.

[opie]

Mikebe,
We owe you thanks for your research. I, also, seem to go to 'blender' mode above 3500 RPM. I will try to get a different prop as you explained above. But, I also will take the time to check out and/or rebuild my carburetors as I hear that if they are clogged somewhat they may restrict flow above a certain RPM. I am smooth as silk up to 3500 RPM and then I either grab "air" with the prop or loose power as I get a definite "surge" from the power department.