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Author Topic:   Motor mounting on Classic 13
lucky 13 posted 06-06-2002 12:04 PM ET (US)   Profile for lucky 13   Send Email to lucky 13  
I just bought a beautiful classic original 13. Long before I found this page I began to envision a 50 hp motor and a center console. I purchased a used 50 merc(2 cyl,2 stroke) with tilt trim and mounted it without giving enough consideration to shaft/transom height. At first it was a disaster. My sea trials ended with a "continuous wave" over the back of the boat swamping the motor well. Obviously I had put a long ahft on a short transom. I raised up to the highest bolt hole adjustment, giving me a 1.5 gain and I added a Dole Fin. This greatly improved the performance. Although it works pretty good now, I see that there are transom jacks used on lots of these boats pictured on this web site. I am thinking about puting one on.

The question I have is:

How do you determine whether your engine is a short shaft or a long shaft? (where are the references that you measur from) IS the cavitation plate the part that I mounted the dole fin to and is this supposed to be at the same depth as the keel? Also, What's a smirk? Any sugestions on which transom jack and where to purchase?

Thanks in advance to any answers.

JBCornwell posted 06-06-2002 02:40 PM ET (US)     Profile for JBCornwell  Send Email to JBCornwell     
Hey, Lucky.

You have overpowered your boat. If it has a console, it was rated for 40 crankshaft hp. If it is tiller, it is rated for 20 crank hp.

BAD idea. You have too much weight on the transom, and too much thrust for the boat design. Your safety is in peril.

Swap that anchor for an engine that matches the design and specs of the boat.

Good luck.

Red sky at night. . .
JB :)

Bigshot posted 06-06-2002 03:19 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Ok Father Horespower:)

To answer your question....what year is the boat? Is it blue inside(or was)? Does it have the "bulkhead" going across the stern or does it have a splashwell that looks more like a bathroom sink molded in? Doe the transom hve a notch where the engine mounts or is it straight across?

If bulkhead you have a pre 1972 and that is short shaft and NO smirk. If you have a tan inside or a 1972 blue hull, then you have a smirk bow(kinda like an upper fat lip under the rubrail) and a 20" transom. If you have an older blue and a 20" engine you might want to reconsider. The drag is VERY stressful on that transom which is 30+ years old. Plus you are trying to get blood from a stone, putting a 50 on a 13 will maybe gain you a couple MPH and will certainly get you to the Chiropractor faster than a 30 or 40 hp.

lucky 13 posted 06-06-2002 04:21 PM ET (US)     Profile for lucky 13  Send Email to lucky 13     
Hey guys,

Thanks for your advice.

Based on your description, I have an older hull (No.2A0316) which is not part of the numbering sequence given in the FAQ's section. The inside is blue and there is a continuous bulkhead across the back forming the engine well.

Horse power aside, I don't think that this 185 lb engine weighs much more than many of the repowers I have read about. Will raising the engine on a lift (like the one on catacea 56) resolve this problem without puting excess drag and stress on the transom? I use the boat on a lake for fishing (no serious horse play) and I want to be able to have good reliability and carry my fat fishing buddy without having to paddle. I'm sure that I could acheive all of the above with a 30, 35 or 40 hp but I stumbled across this one and got a great deal (used).

Getting back to my original questions:

I am having a hard time determining whether this actually is a 20 inch engine. As I mentioned, the performance is pretty fair now that I have adjusted it upward. I can still go up some more. The jacks will perhaps resolve the length issue. I'm not trying to break the sound barrier either. I just want to know how to make the best of a bad situation.

Additionally, I will need to be educated on this if I change out the 50 for less hp and will need to advertise the fifty as either long or short.

Can anyone tell me where to measure to determine the engine lenght?

Highwater posted 06-06-2002 06:27 PM ET (US)     Profile for Highwater    
Assuming that the transom has a "notch" in it, your pre-1973 13' Whaler was designed for a 15" shaft. If you have a motor with a 20" shaft hanging on the back, the cavitation plate will be about 7-8" below the bottom of the hull. If so, you might consider raising it with a jackplate (with as much height and as little setback as possible) or use the CMC vertical extensions. See for both of these options. This will allow you to run in more shallow water, increase your fuel efficiency, and increase your top-end speed.

My 1987 40 hp Johnson weighs 198 pounds, so it weighs more than engine. My boat is not back heavy, but I keep a 12-gallon low-profile Tempo gas tank under the forward seat. If you are so back heavy that you regularly take in water, your hull may be water logged.

If you want to be able to get on a plane carrying more than 800 pounds, you might want to keep the 50 hp engine on it. There is a risk that someone might drive the boat too fast resulting in an accident or worse, and it is from personal experience with such a tragedy that JBCornwell urges us to not over-power our boats. Even so, when I repower I intend to put a 202-pound, 4-stroke Honda 50 hp motor on the transom since it is exactly the same weight as the Honda 40 hp.

Best of luck.

Highwater posted 06-06-2002 06:33 PM ET (US)     Profile for Highwater    
I meant to say, my 40 hp engine weighs more than your 50 hp engine, and I am not back heavy.
jimh posted 06-06-2002 06:36 PM ET (US)     Profile for jimh  Send Email to jimh     
Re Hull Number: you can deduce your model year from the hull number by consulting the list at . Your boat number pre-dates the federally required HIN number which began c.1972. There is a link in the FAQ that points right at this information and mentions this specifically.
Tom W Clark posted 06-06-2002 06:43 PM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
lucky 13,

Your boat is a 1969 model (see: )

Your motor is almost certainly a 20" shaft. You need a 15" shaft motor or some method of raising the motor mount if you want to use the motor you have now. There are lots of options here.

To answer your questions, if you measure your motor from the motor mounting or clamp bracket to the cavitation plate it will be somewhat greater than the shaft length of that motor.

For example, I have both 15" and 20" shaft length motors sitting in my basement now. The 15" shaft motor measures about 17" from the mounting bracket (where the top of the transom would be if it were just hanging on the transom) to the cavitation plate. The 20" motor measures about 22".

Generally speaking the cavitation plate is supposed to be able to be in the water below the level of the keel if the motor is mounted in its lowest position, but mounting hole options allow you to raise the motor to positions where the cavitation plate is above the water. Where you end up with it depending on your boat and the type of boating you do. Like all things, it is a trade off. But you do not want a 20” motor on a 15” transom.

Regarding putting a 50 hp on a 13’ Whaler which has a 40 hp rating, don’t worry about it. This is a very common motor and boat combination. The 13 will handle it fine.

You can read about a 13’ with a Merc 50 here:

jimh posted 06-06-2002 06:47 PM ET (US)     Profile for jimh  Send Email to jimh     
It is also possible that the 50-HP engine is powerhead rated and does not really deliver 50-HP at the shaft as a modern engine would.

It could also be a little tired and not cranking to full rating, too, which would also tend to limit its horsepower.

I think weight is more of a consideration. Heed Clark's advice, he has much experience with smaller Whalers and shallow water.


andygere posted 06-06-2002 07:12 PM ET (US)     Profile for andygere  Send Email to andygere     
I used to run a friend's 70 '13 with a 2 cyl Merc 50, and while performance was brisk, it wasn't unsafe. If it's an older motor, it's putting out less than 50, which is only developed at wide open throttle anyway. Solve your shaft length problems with a jack plate or a shorter leg and go have fun.
lucky 13 posted 06-06-2002 07:19 PM ET (US)     Profile for lucky 13  Send Email to lucky 13     
Hey guys,

I just got back from the local boat and outbourd motor shop. The engine I have is a 15 inch (short shaft). The cavitation plate is exaactly where it is supposed to be and my performance issues appear to be prop related. The boat is not back heavy in the water either, i.e. no weight issues or waterlogging (boat is in really fine shape aside from usual gel spider cracks). The Outboard Guru told me that the basic difference between my 50 and lesser hp models is primarily carburation. Derating this 50 could be a pretty simple task however, he did not recommend this. In general, I am a safety conscious person. Good advice though to be careful about about excessive speed in these fine little boats.

As I mentioned in an earlier thread, my plans are to put a center console in this boat. I have placed an order with Scotty's Marine Outfitters for the Todd marine console with rail and wind screen. I also purchased an igloo 72 qt with cusion for a seat (behind helm ( and a smaller one with cusion for extra seat or storage in front of the console. Additionally I have purchased a new Teleflex cable steering system and 13.5 inch deastroyer helm and a tach which just arrived today from Surplus Unlimited. I'll be sure to post some before and after pix. I'm sure I'll get a lot of booing and hissing when all of you see just how original this boat is before I pervert it I mean convert it. I have plans to use the fine woods that make up the benches and console to trim it and to make cleats to secore coolers, consoles etc. I will post any remaining unused parts on the appropriate forum page if any of you need original steering parts.

Thanks to all who commented. This is a great site and I'll be on here frequently. Look for my next series of questions on how to prop this thing and where to get mental help when symptoms of whaler fever occur.

Bigshot posted 06-07-2002 11:07 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
I thought all post 1980 50hp 4cyl 2 stroke Mercs(classics) were 20". What are the newer 50's, 3 or 4 cylinders? Are they a punched out 40 or a detuned 60?
lucky 13 posted 06-07-2002 11:37 AM ET (US)     Profile for lucky 13  Send Email to lucky 13     

The engine I have is a 2 cyl 2 stroke. The engine is really a Force but with Merc logo. I think in the late 90's Merc bought Force and incorporated many of their parts such as ignition system etc.

Bigshot posted 06-10-2002 09:38 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
OH! Good Luck.
jimh posted 06-10-2002 11:47 AM ET (US)     Profile for jimh  Send Email to jimh     
[Edited TOPIC--jimh.]
lucky 13 posted 06-10-2002 03:51 PM ET (US)     Profile for lucky 13  Send Email to lucky 13     

What does your reply "edited topic" mean?
Just Curios.

lucky 13 posted 06-10-2002 04:08 PM ET (US)     Profile for lucky 13  Send Email to lucky 13     
Big Shot,

I sense that you have reservations about the use of this motor. I think, though, that I will be better off with this rather than a paddle. When I origianally set tout to repower my 13, I chose a Mariner 40 with no power trim. It was hanging on the used rack at the local boat shop. I asked how much and decided to purchse this motor. The owner said " I need to tank test it" before I could walk away with it. He refused my offer to pay for the unit until it was tested. I came back to inquire the next day and the motor was sold to some other "lucky" guy. To make good with me, the boat shop owner gave me an almost new (47 hrs) 50 hp merc/force for the same price. I paid almost nothing. Meanwhile I will be shopping the boat show for a new one at the beginning of next season. I'm considering another Mariner or Yamaha.

Bigshot posted 06-11-2002 10:49 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Run the snot out of it until she goes south, you will probably want to move up to a bigger whaler before then. 13's are great but 15's are better:) Force engines are nobody's favorite and being it is a force she is only producing about 40hp anyway. Does not mean it won't give you 10 years of happiness though. If you want to buy a new mariner, you better shop overseas because they are export only since 2000 I think.
Taylor posted 06-12-2002 01:58 PM ET (US)     Profile for Taylor  Send Email to Taylor     
Lucky 13 - Jim sometimes changes the topic lines to match the contents, particularly if the contents evolve during the discussion. That helps the rest of us find the right info later. This is value added on the part of a moderator. Part of the process requires that he post a reply to incorporate an update or change. That's why you sometimes will see [administrative post]

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