Moderated Discussion Areas
  ContinuousWave: Whaler Performance
  measuring shaft length

Post New Topic  Post Reply
search | FAQ | profile | register | author help

Author Topic:   measuring shaft length
Wet Foot posted 01-27-2003 06:37 PM ET (US)   Profile for Wet Foot   Send Email to Wet Foot  
How do you measure the shaft length of an outboard motor? I was told to measure from the top of the cavitation plate to where the motor sits on the transom. I measured my 4.5 and 85 hp Mercury's and expected to get 15 or 20 inches...I got 18 and 19 inches. I want to mount a kicker bracket before I purchase the motor, and this measurement is critical. Are all outboards 15, 20, 25 inches? The Honda web-site does not mention these dimensions. I have a 2001 Dauntless 18.
Sal DiMercurio posted 01-27-2003 09:05 PM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
Thats the correct way to measure the shaft.
Your engine [ the 85 ] has a 20" shaft, 19 is considered a 20" or long shaft, the 15 is a short shaft, the 25" is anm extra long shaft & the 390" is an extra, extra long shaft.
You antivent [ cavitation ] plate should be close to 3/4" "ABOVE" the bottom of the boat with a normal prop, but the engine can be raised higher as long as the prop dosen't blow out, if it does blow out, you need to get a high performance prop or even a surface running prop, so don't sweat the 1" difference from the 19" to the 20" .
Sal DiMercurio posted 01-27-2003 09:07 PM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
Please excuse the typos, I was on the phone & someone was knocking on the front door, tryed to rush it through.
Tom W Clark posted 01-27-2003 09:49 PM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
Wet Foot,

Yes, all outboards are designated as 15", 20", 25" or even 30" shaft lengths but the measurement between the cavitation plate and the top of the motor mount will not necessarily equal these numbers. It will be somewhat greater.

A 15" shaft motor will measure about 17" - 17.5" and a 20" shaft motor will measure about 22" - 22.5" so your 4.5 if definitely a 15" motor. The 19" measurement of your Mercury 85 is a bit more puzzling. If the motor is older I would suspect it is a 15 (short) shaft motor, but a 19 measurement seems far too much for a short shaft. What year is the motor?

Usually the cavitation plate is designed to be below the water level if the motor is mounted all the way down. If you want the cavitation plate above the water lever, that is what the four extra mounting holes are for. You raise it up in 3/4 increments.

Bigshot posted 01-28-2003 08:40 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
It is for his kicker. Get it level with hull bottom. I would do the old hold and mark but make sure the lift is in the lowered position.
Wet Foot posted 01-28-2003 11:15 AM ET (US)     Profile for Wet Foot  Send Email to Wet Foot     
Thanks Guys! My 4.5HP is a 1978 Merc. and my 85HP is a 1977 Merc (I'm selling them both). I am buying a Tanner Manufacturing kicker bracket for my 2001 18 Duantless and figured I would mount the bracket in the best location (for reaching it and avoid bumping main engine). Is this a mistake? Should I buy the kicker motor first?
Bigshot posted 01-28-2003 11:24 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
I would use the 4.5hp and see how it does. Just get a high thrust prop. If it can move a big sailboat, it can move a 18' dauntless although I think an 8 would be ideal, I would try the 4.5. Problem with the 4.5 is she is only a single so torque might be lacking. Try and mount where you can get a connecting rod to steer the kicker from your wheel.
Tom W Clark posted 01-28-2003 12:50 PM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
Wet Foot,

Both your old motors are 15" shaft motors.

You would be well advised to have both the kicker and the bracket before you start drilling holes.

Are you going to use the Tanner fixed bracket?

You definitely want to get a 20" shaft kicker. This will help keep the powerhead out of the water when it is rough out. I use an Evinrude 20 shaft four stroke as a kicker and it measures 22.5 between the cavitation pate and the mounting bracket.

Do not worry too much about lining up the cavitation plate with the bottom of the boat, just be sure it is at least as deep, if not deeper than the bottom. In rough water a boat can see-saw over a wave and lift the kicker's prop close enough to the surface for it to suck air if the kicker is not set deep enough. This can be annoying while trolling.

Wet Foot posted 01-28-2003 04:00 PM ET (US)     Profile for Wet Foot  Send Email to Wet Foot     
Tom and others,

I'm ready to purchase the Tanner fixed bracket that Whaler suggested. My friends recommend the OMC bracket with piston assist. They say it's easier to raise the motor then tilting; even though they tilt for long hauls. I don't see a problem tilting a small outboard and I think the Tanner will look better and last longer (no moving parts). Any other suggestions before I make the purchase?

Wet Foot posted 01-28-2003 06:21 PM ET (US)     Profile for Wet Foot  Send Email to Wet Foot     

I was reading another reply from you on kicker motors and you said to attach it directly to the transom (no bracket). I'm assuming that those boats have a wider distance on the tramsom, where a motor can be hung. Will that technique work on my 18 Dauntless? I think my narrower transom "cut-out" prohibits this and I need a bracket. Am I missing something here?

Tom W Clark posted 01-28-2003 08:53 PM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
Wet Foot,

Clamping the kicker directly to the transom is not an option on your Dauntless 18. There's simply not enough room.

I think the Tanner fixed bracket will ultimately be a little stronger than an articulated bracket, but if you DO get an articulated bracket, the OMC one is far superior than any other on the market. That doesn't mean another wouldn't work fine, but the OMC bracket is just a better engineered piece of hardware.

By the way, your Mercury 85 hp is a 20" shaft motor. I stopped at a boat for sale this evening on my way home and saw it had a 1971 Mercury 80 hp on it. I measured the distance from the cavitation plate to the top of the transom. It measured 19". The cavitation plate was exactly like Sal described it, about 3/4" above the bottom of the hull.

Arch Autenreith posted 01-28-2003 10:34 PM ET (US)     Profile for Arch Autenreith  Send Email to Arch Autenreith     
Tom. I spend a good 10 minutes looking for the OMC articulated bracket you specified and can't find it. Do you happen to have a link?
Tom W Clark posted 01-28-2003 10:57 PM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     

I don't know if they are still called OMC brackets since Bombardier took over. Heck, I;m not sure they are even made anymore, but I would think so. The have made them for so long and have the reputation as THE auxiliary bracket that I would expect them to be made by someone.

I know they have them on the floor at Jacobsen's Marine here in Seattle 206-789-7474 and at Sea-Way Marine

They come with synthetic mounting boards now instead of the varnished plywood and there is even an extra heavy duty model that is rated for something like 20 hp. They are not cheap. I have seen them priced as high as $450.

Wet Foot posted 01-29-2003 11:35 AM ET (US)     Profile for Wet Foot  Send Email to Wet Foot     
Thanks Tom!!

So which one would you buy, Tanner or OMC? Will tilting an 8 HP 4 stroke be difficult? I've heard that pushing the OMC down can be hard when you can't be directly above engine. I would hate to choose the wrong one!

Arch Autenreith posted 01-29-2003 11:58 AM ET (US)     Profile for Arch Autenreith  Send Email to Arch Autenreith     
Oops...missed your post. Thanks Tom.
Sal DiMercurio posted 01-29-2003 09:08 PM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
I'll be real honest with you, I,v gone through 2 omc brackets for my 15 kicker, & 3 omc pistons that push the bracket back up from the down position.
The piston is definetly a weak point on their brackets, plus they are about $80.00 each time they go out.
I finally got disgusted & just hung the engine on the trasom, thing I could have done.
When your kicker is on a bracket, it "REALLY" takes a beating when the weather is choppy & when the boat is on the trailer.
My advise to you is just mount it on the transom on the port side of your main engine, as far out to the side as you can get it, the reason to mount it way out to the side is, the deadrise of the bottom allows the prop to get below the bottom the farther out you go.
The antivent [ cavitation ] plate dosen't need to be above the bottom, as the little engine will vent or cavitate far easier in sloppy water then the main engine because the prop is so small, it breaks free as soon as even the tip of the prop breaks the surface.
It's very easy to control the boat with just the kicker running & steering with the big engine shut off, just point the kicker straight & the bigger lower unit on the big engine will steer the boat just fine.
I would try it right on the transom before buying a bracket.
The brackets aren't cracked up to be what they are supposed to be.
Believe me, your engine will be bouncing all over on a bracket.
Tom W Clark posted 01-30-2003 02:09 AM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
Wet Foot,

Either way will work fine. If it were me I would get the Tanner fixed bracket because it will probably be stronger and less expensive. The one thing you need to be careful of with a fixed bracket is that when the kicker is in the tilted (stowed) position and you are running in rough water, the kicker can bounce up and down and either bounce out of it's tilt lock or sheer the tilt lock off.

The way to prevent this is to either use what is called a trailering bracket (and if you are getting a Honda, I don't know if Honda makes such a thing) or simply tie it down so it cannot bounce.

The first kicker I had was a Johnson 6 hp on my second Montauk and it locked in the tilted position but it could not take the bouncing and I sheered the tilt lock pin off the first time I ran the boat. After that I used the OMC trailering bracket which replaced the tilt pin with a flip up bracket which allowed the motor to lock onto it as if it were the tilt pin with no play.

Bigshot posted 01-30-2003 09:21 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Sal you really do NOT read these posts do you? I do agree with what you are saying 100% but....

This was already discussed and as quoted by Tom: "Clamping the kicker directly to the transom is not an option on your Dauntless 18. There's simply not enough room."

Post New Topic  Post Reply
Hop to:

Contact Us | RETURN to ContinuousWave Top Page

Powered by: Ultimate Bulletin Board, Freeware Version 2000
Purchase our Licensed Version- which adds many more features!
© Infopop Corporation (formerly Madrona Park, Inc.), 1998 - 2000.