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T.KAMILA
03-15-2002, 04:54 PM
I just purchased a 4 HP Evinrude Yachtwin for my 15’ catboat. The question is, what is the best way to mount it to the transom of the boat? The shaft is twenty-two inches and the transom from the top to the waterline is twenty-four inches. Do I need a lifting type bracket or a non-adjustable type? What should I be considering here?

Thanks,
Tom

Roger Stouff
03-15-2002, 06:36 PM
Tom,
I'm sure you'll get plenty better answers soon than I can give you, but I'm just curious: What kind of catboat is it? I just got plans in for a 15' Marsh Cat.

R

blisspacket
03-15-2002, 09:46 PM
Some considerations: appearance-wise, they are all ugly. You'd have to consider the level of ugly with the prop pendulumed out and back versus elevating it on a swinging bracket.

Either method probably will present opportunities for the mainsheet to tangle with motor appendages.

The aluminum bracketed motor raisers often have narrowly spaced bar stock. If, as I do, you manipulate the tiller of the outboard for close quarter manuevering against wind and tide, you might pretzel the bar stock if you go wild with the throttle. I've seen stainless tube stock, widely spaced, motor brackets, that could withstand that torsion (i.e. when outboard it at 90 degrees to transom) better.

There will be times when there's enough chop that an outboard on ANY bracket is far enough aft that the prop will catch air; even when the prop comes close to the surface it can cavitate, and continue whining until you throttle down and then back up.

When wind and tide are against you an outboard sure beats rowing....

yachtdoc
03-16-2002, 10:25 PM
hi tom:

you did not give many details of hull, (glass or wood) etc. If it were me, I would think about a rudder mount or (best) an inboard well, usually under the stern seat.

Jim Reynolds

T.KAMILA
03-17-2002, 06:22 AM
Roger the boat is a Wittholz 15’ plywood catboat re-lofted to round bilge and stripbuilt. I have been following your post and can relate to what you’re going through. The Marsh Cat is a nice boat and Buddy Sahrpton has given a lot of thought to his modifications.
Jim I have had the idea of an inboard well in the back of my mind but have never seen one in a catboat this small. It also would look much nicer.
Blisspacket thanks for the heads up about the flimsy construction of some of the brackets. I was planning on fabricating my own if it didn’t need to adjust up and down.
Jim could you elaborate on the rudder mount configuration. That locates the motor close to the centerline of the boat and as you know the catboat has a substantial rudder.

Thanks Tom

Buddy Sharpton
03-19-2002, 07:16 PM
Sounds like you're close to launch - congratulations.

I bought a stainless steel two postion up/down bracket for my Marshcat and c-clamped it to the transom to find ideal mounting position for my two horse 4 stroke Honda. Concluded it was too ugly. It's yours if you want it.

I have a mahogany motor pad doubler on insde of transom with circular "sockets" counterbored to postion motor quickly to vertical on the transom, 14 inches out from centerline to port. The long shaft puts prop above my rudder's endplate and a plywood tab on the cavitation plate keeps the prop from striking turned rudder.

My mainsheet lower block rides on a bronze bar horse across the middle third of my transom. Yeah, the mainsheet needs attention not to hang up on the motor head.

The fix is to put an eyestrap under the deck, at the edge of the coaming, about a foot forward of the transom. Rig a rope traveler with two clips and, put it in place and move the mainsheet block's shackle to it. Sheet will not foul motor, or be in crew's way. Motor is still ugly, up high and loud, but bearable for short hauls.

Real fix, make a wooden bracket to rig first, then put on motor with powerhead wel aft of transom and lower than top of transom. You can't see it from inside boat, it's much quieter in use, and you can use that nice bronze horse again and put away rope traveler.

I made one out of mahogany , a horizontal 3 x 3 beam about 14" long with a 1 1/2 thick motor pad at the outboard end. A vertical 3/4 3' piece is fastened to the inboard end along with a 10" wide 3/4 x 2 horizonbal beam below. Two triangular side cheeks of 3/4 mahogany keep that angle from opening under the 30 pound weight of the motor. A bronze angle iron overlaps the top of the transom with a 1/2" bronze bolt pin that fits into a standard bronze oarlock socket mortised into transom. The other socket is to starboard so I can skull off the stern one handed with an oar.

A 3/8" hole is drilled thru vertical piece of bracket, transom, and inner pad . A toggle boat pins the works in place and a wingnut snugs it up A bronze washer glued on inside pad around the hole keeps the toggle from chewing uo the inside of the transom. The bracket has three point bearing on the transom and is quite rigid.When you remove bracket there's only an itty, bitty 3/8" hole 8" above the waterline to see in transom, and a wooden dowel plugs that.

You have to play to get the dimensions so that when tilted down, the cavitation plate is below rudder, and when tilted up, there's room for the motor head to clear the bracket and prop to be clear of water. It can be done so the motor "works" properly both on the transom edge, and on the bracket. For longer hauls< I really like using the bracket. It's a quieter ride, and the bracket being properly bunged and varnished, blends in with the wooden transom and looks pretty good. Keeping the motorhead lower, up or down, definitely helps looks of the silhouette of the boat.

Done this way, you don't need any verical travel for the moter like an adjustable bracket provides, and those bracket do lift the motorhead so high. That being said, on the adjustable bracket you can raise the motor , tilt it up, and then lower the bracket again so motor's skeg barely clears/drags in water, and head is not so high. But when you remove motor, you've still got the bracket, or at least some kind of mounting plate spoiling the transom. At least to my eye. Too fussy I guess.

T.KAMILA
03-20-2002, 05:43 AM
Buddy,
Nice to hear from you. I think you deserve the title of “Forum Guru of small Catboats”. Your Idea sounds good. The thing I need to know before I can design a single position bracket is the depth of the cavitation plate below the water line in the down position. How far down and how far aft is yours. I assume that the further aft it is the greater tendency to cavitate when bouncing around out there.

Tom

Buddy Sharpton
03-20-2002, 11:16 AM
Tom, I'm gonna build you a watch. When motoring, a prop pors out of the water as much from the roll of the boat as the pitch, especially in a quartering sea. The closer to centerline the better, but with an outboard rudder that means offsetting the motor to tha side only as much as you need to clear the motor when the rudder swings. On a tall narrow rudder, no problem, On a wide, shallow barndoor catboat rudder, you have to compromise, allow for maybe 40 degrees swing and arrange some sort of guard or tab on the motor to fend off the rudder with something other than the spinning prop.

Sometimes people actually put the motor mount on the side of the rudder, solving both problems in a very workable arrangement.I made a test rig of this for my Marshcat. I like real sensitivity in my tiller-on a balanced rudder you can achieve it; on a rudder hinged at the leading edge, much less so, Add the extra mass of the motor and the helm felt vague and heavy to me, motor running or not- just too much mass on too long a moment for good feel.

Hull drag has two components- wave making resistance and frictional drag.

On a planing hull, the depth of the cavitation plate is critical- it should be about a inch below the bottom of hull to minimise unnecessary drag from the lower unit. Frictional drag is the much bigher factor on planing craft.

The catboat is a displacement hull. As it moves faster it pulls up a bow wave forward, a stern wave aft, and digs a hole around the middle of the boat. Climbing up that bow wave IS the wave making resistance we're talking about and the catboat won't do it, overcome the resistance , get over that bow wave and run ahead of it That's planing. Maybe for a few seconds surking down a wave, but that's propelled by gravity, not sail power or engine power. So drag is much less an issue. Thus it is desirable to pbut the prop as deep as you figure it will need to be to not come out of the water as the boat bobs. Motors in wella are always carrying the foot of motor well below surface. Saildrives are below the bottom of the hull just aft of a fin keel.

The other side of the consideration is while the foot is located deeper, the powerhead is getting closer to the water too, so you don't want to be so low as to get the nmotor dunked under when the boat bobs.

The boat will squat down at the stern a few inches under power so that will get your prop deeper still when the motor is in use.

Screw your mount to a board you can c clamp to the transom, at least in the shop, better yet for an in the water test before you drill "real" holes, and experiment. Clearing the rudder, having room to tilt up motor and clear transom with the powerhead and the water with the foot are all more important factors than depth of cavitation plate. With a long shaft, that's not going to be a worry. Not having the foot still drag on a long shaft when tilted up is much more of a worry. Thats unnecessary drag under sail, ouch. Thats why folks like the up,down "scissors " bracket because with 11 to 14 inches of vertical travel, a regular shaft motor can be deep enough down, and high enough up, when tilted.

Having said that, using my bracket,the bottom of my long shaft motor power head is about 8 inches out of the water, and the cavitation plate 11' below water. Mounted on the transom, my powerhead is 20" above the water, and the cavitation plate right at the water line. But underway under power because thare's not enough wind, the prop stays submerged well enough. If it's really blowing and the water is rough- I'm going to be sailing anyway, aren't I?

That's what I know works on mine.

T.KAMILA
03-22-2002, 05:37 AM
Thanks Buddy, I think I have enough to make a go of it. I'll let you know how I make out.

Tom