Kicker speed?

Helen O · Posted: Tue Dec 02, 2003 9:05 pm Post subject: Kicker speed?

How fast does your kicker motor push your boat? If you're running twins, how fast will one of your twins push it?

Helen O · Posted: Tue Dec 02, 2003 9:13 pm Post subject:

My 15 hp long shaft Honda kicker will push my CD25 between 6 and 7 mph. Measured on the Columbia by gps on the incoming tide. Traveled up and downriver to make sure the current wasn't a factor.
Tyboo Mike, I'm curious to know how much difference the extra long shaft 15 hp kicker makes on your boat.
Oh yeah, I wasn't running mine at complete open throttle, but close. I don't like running wide open for long lengths of time.

TyBoo · Posted: Tue Dec 02, 2003 9:23 pm Post subject:

The 8hp Honda on the TyBoo22 pushed it for about seven miles toward Friday Harbor at right around 6 knots at 3/4 throttle.

If Les' mechanic gets the pisser working on the 15hp Honda hanging so far down off the stern of the TyBoo25, I'll let you know what she does.

Flat Iron · Posted: Tue Dec 02, 2003 9:24 pm Post subject:

Larry S

Just recently did this test with Flat Iron on Lake Powell, AZ. with my twin 40 Yamaha's. At a lake elevation of 3600ft. I only got up to 8.9mph with just the one engine at 3700rpm with a heavily loaded boat.

Dan and Jan on Flat Iron

JoeP · Posted: Wed Dec 03, 2003 10:03 pm Post subject:

Miss Mirth (22') gets 5 1/2 to 6 mph with a 8HP Yamaha at WOT.

Chuck S · Posted: Thu Dec 04, 2003 7:33 am Post subject:

Anyone tried a low pitch propeller?

Unless you can get the boat on a plane the speed will be limited to hull speed regardless of horsepower. That's ~5-6 knots on this length hull. I could push my 4000+ pound J/24 sailboat to 6 knots with a 4.5HP Johnson outboard, even with the 4' fin keel sticking down from the hull. This had a "workboat" not "speedboat" propeller on it from the 9.9 Yacht engine as I recall, the dealer set it up and it worked very, very well.

I'm thinking the folks with twins may have some luck with a lower pitch spare propeller. Changing a prop at sea is pretty much impossible, but losing an engine on the beach and needing to get home on one has some potential. Letting the engine rev higher than Dan's 3700 rpm might get the boat on a plane and will instantly double the get home speed.

What propeller you guys running on the auxillary engines?

-- Chuck

Sea Wolf · Posted: Thu Dec 04, 2003 8:37 am Post subject:

Chuck- Changing the pitch on a kicker motor is good for the motor, but only results in minimial speed gains. Doing so on a 40-50 hp twin main may produce some real results.

On my CD-22 Cruiser, I changed the prop on my 15 hp Johnson 2-cycle kicker from 10 to 5 inches and it really benefited the performance the motor. Instead of lugging out to a peak of about 3000 rpms (judged by sound-w/o a tachometer), the motor will now fully wind up to about 6000 rpm. The big benefit is to the engine, which can now rev up easily and not lug, blow out unused oil, and foul plugs, etc.

But the speed changes little, from about 6 to maybe 8 mph. The boat is still very much trapped in displacement mode and won't climb up on the bow wave and plane, but instead just goes a little faster and mostly drags a bigger wake. This is probably why limiting a kicker to a 8-10 hp max is the usual thing to do. Going to a sailboat style "bigfoot" auxillary that has a lower gear ratio and a larger, lower pitched prop is a much better set up as far as energy (really momentum) transfer is concerned, but displacement speed is displacement speed, as you know. We sailboaters understand this well.

I think you're right about the possibility of getting minimal or slightly better planing performance from one of a set of twins. From my handling experience with the CD-22, climbing up to get the boat on step at the beginning of the planing mode would seem to take about 40-50 hp, roughly judged. A single motor of a pair of twins with the right switch in props might just be able to get much better up into and beyond the 9-11 mph range where planing initiates and continue (if not to heavily loaded, of course), but then one would be have to be able to change props and be willing to run up near or at the maximum rpm continuously to do so. It would be great if someone has the extra low pitched prop to try this out. Joe.

Helen O · Posted: Thu Dec 04, 2003 8:50 am Post subject:

I have a low pitch prop on my 15. I have to be careful not to over rev the engine. That's not the biggest problem.
The major problem with a kicker is that it doesn't sit and push on the center of the stern. It's way off to the side, even more so than twins. This causes it to not track in a straight line under speed. I have to compensate with steering which causes the boat to travel in an small "S" pattern. Does that make sense?

Sea Wolf · Posted: Thu Dec 04, 2003 1:02 pm Post subject:

Helen O: Do you have a cross connecting steering bar so that you are steering with the main motor and its skeg still in the water? The main motor skeg and the small keel down the center of the C-Dory help track the boat, although in chop and swell you'll be over-compensating with the steering and may find that the 15 is basically unstable when the motor's that far off center and the pitching forces and/or wind eventually become overwhelming. Does your C-D 25 have a center keel like the 22? I've never had signifigant problems steering straight in moderately winds or small chop in my 22 with the 15 on the starboard side, but still mounted inside the motor well. Is your 15 mounted on a bracket much further off center? What types of conditions bring about the "s" steering wandering problem? Do any other C-D 25 owners experience this? Over-reving isn't too much of an issue, as it gets so little extra speed in the righer rpms that it isn't worth the trouble to wind 'er up past about 3500 (at least for me). Joe.

Iconoclast · Posted: Thu Dec 04, 2003 1:14 pm Post subject:

If a single 40 hp on the twins can't make a 22' plane, why are twins recommended at all? (Other than ability to trim for lateral balance.) From a reliability standpoint, what's the difference between motoring home with a 9.9 kicker and a single 40?

Helen O · Posted: Thu Dec 04, 2003 4:42 pm Post subject:

Sea Wolf

I don't know what a skeg is, but I had the main motor raised up. The connecting crossbar still worked, so I could steer from the helm. I think the bottom of the 25 is the same as on the 22, I can't address the keel issue.

Good question, Iconoclast.

Flat Iron · Posted: Thu Dec 04, 2003 6:58 pm Post subject: Kicker Speed

Iconoclast,

I may be wrong on this but I think this is where the higher torque factor of the 40's and 50's come into play. I had a heck of a time holding a course with my old 8hp in a strong wind and outgoing tide but don't seem to have that problem when running a single 40. Does this seem to make sense....anyone?

Dan and Jan on Flat Iron

Da Nag · Posted: Thu Dec 04, 2003 7:23 pm Post subject:

On Da Nag 19, I noticed a huge difference in "steer-ability" when using the kicker if the main was down - connected to the kicker, of course. The added rudder area of the main is pretty significant.

I realize this tip doesn't do much for folks wanting to steer a kicker with the tiller handle, but in the 19, there's really no reason to do that since the cockpit is so close to the helm. On the 22/25's however, this is another great benefit to the Raymarine autopilot + cockpit remote...

DaveS · Posted: Thu Dec 04, 2003 7:30 pm Post subject:

Bill, does this mean that on a HOT SUMMER DAY, we'll be able to sit in a ski tube in the water behind our vessels and steer around the lakes and the sound by the remotes? Cool!

Flat Iron · Posted: Thu Dec 04, 2003 7:37 pm Post subject: Kicker Speed

Chuck S,

I'm running Yamaha 10&3/8x13's on my twin 40's. Trolling speed with one engine is .08mph and with two engines it's 1.04mph at 900rpm. I use one engine mostly when trolling K-14 & K-15 Flatfish for King Salmon, the speed seems to be just perfect. Also works real well (one engine) when trolling big spinners like Blue Fox, Mepp's others. This is on the upper Sacramento River with little tidal flow.

Dan and Jan on Flat Iron