PROPER SIZING FOR A KICKER MOTOR

bschell · Posted: Sun May 24, 2009 1:59 pm Post subject: PROPER SIZING FOR A KICKER MOTOR

WE HAVE A 2003 22' CRUISER, POWERED BY A SINGLE MOTOR 90 HP YAMAHA FOUR STROKE. I HANG A TOHATSU 6HP FOUR STROKE 20" LONG SHAFT ON THE TRANSOM. WE US THIS MOTOR MOSTLY FOR THE TENDER, BUT I HAD HOPED IT WOULD ALSO PUSH THE BOAT IN CASE OF MAIN ENGINE FAILURE, BUT IT JUST DOES NOT HAVE THE POWER!
MY QUESTION, WHAT WOULD BE THE PROPER SIZE KICKER FOR THIS BOAT TO GET US BACK TO SAFE HARBOR IN CASE OF BREAKDOWN.
I WOULD RATHER NOT USE A BOLT ON ENGINE MOUNT, I WOULD PERFER TO JUST HANG IT ON THE TRANSOM, BUT I KNOW THIS MIGHT NOT BE SAFE OF PROSSIBLE. ANY INFO WOULD BE HELPFUL!

BRIAN

dotnmarty · Posted: Sun May 24, 2009 2:37 pm Post subject:

Check out this thread

http://www.c-brats.com/viewtopic.php?t=10933

MartyP

thataway · Posted: Sun May 24, 2009 4:00 pm Post subject:

What do you mean it does not have the power? 6 hp should push the C Dory easily at 4 1/2 to 5 knots. 6 knots is the max easily driven displacement speed (1.34 x 4.47 (sq root LWL)) If you go to 8 hp and a big foot you may get 7 knots. but 7 knots is over what you expect for a displacement speed.

I have posted this before, but I grew up on a 26 foot sailboat with a 5 hp outboard, as its only power. That boat had considerably more resistance than either a c Dory22 or C Dory 25, because of the large fin keel, although the bottom was almost exactly like the C Dory (arc bottom with hard chine). It was slow, but it always got there. There were 6 hour trips to Catalina. The kicker is an emergency get home engine.

For more "thrust" you can go with a lower pitch prop, at max diameter for that 6 hp, or a 8 to 9 HP "Big foot"--which allows a larger prop. Although a 6 hp long shaft. can be used for a dinghy, it is not ideal because it is slightly more difficult to beach, and it will not plane as well as a short shaft (if it will plane the dinghy).

bschell · Posted: Mon May 25, 2009 12:13 pm Post subject:

HEY BOB,

BEING 45 MILES OFFSHORE TUNA FISHING AND THINKING OF STARTING THE KICKER (IT SEEMS TO SHAKE LIKE HELL AT FULL THROTTLE) IN 2 FOOT WIND CHOP SEEMS A LITTLE CRAZY. MAYBE THE ANSWER IS LIKE YOU SAID, CHANGE THE PROP FOR MORE THRUST.

thataway · Posted: Mon May 25, 2009 3:27 pm Post subject:

You probably should not run the kicker at full throttle. It is probably a function of the mount, rather than the engine. Yes, it might take 10 hours to get back in--but it sure beats rowing.

On the other hand, most outboards are very reliable (if we could just get rid of that darn ethanol!). If you have fuel problems, and use the same fuel tank for the kicker...then you are not really better off! So to be entirely safe, a separate fuel supply would be ideal for the kicker.

Tortuga · Posted: Tue May 26, 2009 1:13 am Post subject:

I've got the same setup -- Yamaha 90 + Tohatsu 6 kicker. While I haven't run it in 2 foot wind chop I have run it in wind and cross currents -- and the little motor certainly does push the 22 -- though not fast. I am confident that if I needed the kicker it would perform as intended. Last summer I pushed the boat with a Nissan 2.5 across the marina -- it did well with no wind, though with no neutral or reverse I had some stress driving the boat onto the trailer.

Since the 6 is a single cylinder motor it does vibrate -- but that shouldn't be a problem beyond annoyance.

In a perfect world I'd probably run the Yamaha 8 high thrust motor as a kicker -- that would accommodate any conditions at displacement speeds -- probably be able to climb up 4' wind waves. But, I'm happy with the 6, and I hate the weight of the larger kickers. Plus, like you, I use the 6 on the dink.

Re having your main motor crap out 45 miles offshore. There are no good solutions -- just a variety of bad ones. Having a large kicker may be better than a small one, but the small one will still get the job done. I had an inboard/outboard (outdrive) suck water into the engine block at Anacapa Island years back (that was the moment I gave up on engines below the water line) -- it took Vessel Assist 3 hours to get to us, and 3 more hours to tow us back to Ventura -- and that was only 17 miles. 45 miles -- easily would have been 8-9 hours under tow.

I suppose if you primarily use your boat that far offshore you would do well to keep a larger high thrust kicker with independent gas -- but you will still only make displacement speed (5+/- knots).

Matt

toyman · Posted: Tue May 26, 2009 1:08 pm Post subject:

I believe that someone with a little sailing in their background could (would) be more comfortable using a smaller kicker than someone who has always lots of H.P.. Sail boats seldom have the power to go directly upstream, or upwind. I have a old (little used sail boat kicker) Honda BF8A that I will use as the kicker on my 25.

bschell · Posted: Thu May 28, 2009 1:37 pm Post subject:

MATT,

SOUNDS LIKE WE RUN OUR BOATS IN THE SAME WATERS, RIGHT ON.
WE MOSTLY RUN TO CATALINA, SAN CLEMENTE ISLAND, CORONADOS,
ENSENADA AND ALL THE HIGHT SPOTS IN BETWEEN PADDY FISHING.
WAS OUT AT THE BUTTERFLY LAST SUMMER BY MYSELF AND THE RECTIFIER AND REGULATOR BURNT UP, THOUGHT I HAD AN ENGINE FIRE. THE SMOKE POURING OUT OF THE ENGINE COVER STOPPED AFTER A WHILE, I LEARNED YOU HAVE TO BE READY FOR JUST ABOUT ANYTHING AT ANY TIME, AND YES, IT WAS ONE LONG ASS TOW BACK TO DANA POINT.

BRIAN