TOPIC: 1965 Glasspar Marathon - Outboard sizing question

Hello all,

I'm new to the forum, and boat ownership in general. I acquired some time ago a 1965 Glasspar Marathon 14" boat with a Johnson 20 HP outboard on it. After having it checked out by a marine mechanic, it was found that the bottom end was frozen and would need another motor.

After some research on the appropriate HP ratings for the hull, I found that this model was designed for a maximum of 75 HP. Through a friend of my brother-in-law I purchased a Mercury 500, 50 HP outboard. As I was doing some research on the Marathon more recently, I came across some posts in a forum indicating that the Marathon requires a "short shaft" motor.

I'm concerned that the motor I have may not be appropriate for installing on the boat, and was hoping I could get some advice here regarding this. Where on the motor should I take measurements to identify if it is sized appropriately for the transom?

I'm including below an image of the engine in case there are different variants of the Merc' 500 I am not aware of.

Thanks in advance for any information you can provide,

Rob

Rob,

Others should chime in here, but this is what I see: the motor appears to be the long shaft (for a 20" transom) measured from where the clamp sits on the transom to the wide/flat ventaltion plate which sits above the water pick-ups (some call this the cavitation plate). Should be easy to see if it is the short 15", or the longer 20". Nice looking motor though Good luck. others - please clarify if I am saying this incorrectly or confusingly.

Dr. Go! (Mark)

Mark,

Thanks for the very quick reply. I've measured the motor and believe that you are exactly correct. I've marked up the photo shown below, which measures 20" to the lowest of the plates on the prop facing side of the motor. There is a wider plate that sits another 2" lower that extends opposite the prop side. Depending on which measurement is correct, the shaft length is either 20" or 22" I assume?

I also measured the transom on the boat. Measuring from the top of the transom to the bottom of the hull, at the midpoint of the transom (widest point) it measures 20".

I had thought I had read that the Marathon was supposed to measure 15". So... did I measure the transom correctly? Is it wrong to assume if the transom measures 20", and the motor shaft measures 20", that I have a match? Or is the motor supposed to be 5" shorter than the transom depth?

Rob

robmohr,

WELCOME ABOARD. - IF the Marathon was mine, I would sell (Your OB looks like a 20" shaft to me.) the long-shaft Mercury 50 & replace it with a matched pair of pre-1970 short-foot Evinrude, Gale, Johnson or Sea King BigTwins.
(A visit to any number of large AOMCI or other outboard/boat swap-meets will likely find a suitable pair of suitable outboards & that won't require you to "raise the transom". - I wouldn't be shocked to find that you can sell your nice-looking Mercury 50 for enough $$$ to buy the BigTwins.)

just my OPINION, satx

If they both measure 20", you have the correct match. You do not want to put a short 15" motor on a boat with a 20" transom for a few reasons: 1. the water pickup may not take in cooling water properly. 2. when trying to get the boat up on-plane, the propeller will likely catch air and ventilate (revving up too high and loosing bite). This in generally for most recreational boating. Boaters "in the know" sometimes raise motors up a few inches, but not 5", for small recreational use, it is best to match 15" short shaft motors with the older/shorter 15" transoms and also use the 20" long shaft motors on 20" transom boats. There are performance people out there that know how to raise motors to go fast and still get cooling. Your situation should just go with stock intentions. You measure your motor correctly. It is also not best to put a 20" motor on a 15" transom: sits very deep for shallow water...or raising the center of gravity 5" is not a good idea either.

satx is right...there should be a good market out there for that nice 50hp merc!

Dr.Go!

Based on the information I found here:

www.leeroysramblings.com/OB_shaft_length.htm

It appears that I should be using the 22" measurement I mentioned above for the shaft length. Also, this would indicate that for a 20" transom height, the recommended shaft length would be 20" (long). This is a bit confusing, as my measurement is 22", which would classify as neither long nor extra-long?

Also, I found elsewhere on this site:

www.fiberglassics.com/library/File:Glassparbb003.jpg

The marathon transom height is defined as "Long". This would lead me to believe that the motor I have is close to the right size, correct?

Rob

Not sure if you saw my follow-up where I measured the actual transom height and found it to be 20", not the 15" that I've seen on the forums.

robmhor,

I believe you have the right motor for your boat. You measured a 20 inch transom on your boat and the Glasspar specs in the FG library say it has a "long" transom.
The 20 inch versus 22 inch measurement on the motor may be a small measurement error in that the transom clamp can swing up and and down and your pic is a little to dark to see exactly where it's positioned. It looks to me like it's too far towards the raised position (out of the water) and if you pin it in the running position it will measure much closer to 20 inches.
You might want to make sure that it is pinned a hole or two from the bottom and then measure it.
As Dr. Go pointed out, a little too deep isn't a real problem, but running a motor to high can cause serious problems.

Don

I also have another question about the boat. I don't know enough about it to know if I should be concerned about the transom or not. On the left hand side of the transom, the tie down point is pulled away and the exposed threads of the bolt show significant corrosion (picture attached). The tie down strap on that side is being attached to a cleat up top , as it would not be safe to use the intended point. The right hand side is solid (also pictured).

When I rap the transom with my knuckle, the middle third to 3/5 of the transom sounds solid. Out toward the sides on both sides it sounds hollow. Is this normal? Do I need to replace the transom?

Rob

Second pic

Don,

Thanks so much for the reply. You've set me at ease that I'm not going to have to sell this motor and get another to replace it. I thought the bracket position might be throwing me off a bit, which you have confirmed. I'll see if I can get another pic that is clearer. I'll lay the motor on it's side so that the bottom tavitation plate is easier to pick out.

robmhor,

Also to add - in 1965, they only made what was considered short shaft = 15" ,and long shaft motor = 20"

if you measured a 20 inch transom, you are good to go. That said, I do not know this boat (where others here do know it). You have a nice motor to use...maybe get expected performance advice from others on this site and determine if that will meet your needs. If not, you have what I would believe to be a marketable motor to sell if others here can offer performance tips on either larger motors or twin motors if that would better suit your goals. Again - I do not know this boat...but what I have heard many times throughout my life is the "I wish I would have put a larger motor on more closely rated to the boat's certified rated horsepower"...for many boats - once they are loaded with people and gear (and even more - if they now want to tow a skier), they wish they had "more power"...maybe this is not the best advice coming from someone who got the nickname Dr. Go! in my 20's because my boat at that time would only go 92mph and I was wanting to see 100...I have since slowed down to 70mph, 54mph, 35mph, and 26mph boats. I am trying my best to kick the speed addiction habit. Best of luck and I will step away and let others give you the finer detailed advice. Welcome aboard - I am new as well.

Dr. Go!

Dr. Go,

Great advice. As the original motor on the boat was only 20 HP, I didn't want to go too big, as it is a 50 year old hull. For my needs, I suspect 50 HP should be more than enough, as I was born the same year this boat was and my Speedy Gonzales days are past me I plan to mainly use it on the lakes and reservoirs here in Oregon for some casual weekend fishing. I'll likely put a small kicker on it for trolling (would love to hear recommendations for vintage options that would match the boat). I doubt I will take it out onto the Columbia river, the people get a bit too crazy out there on the hog lines for my taste.

Rob

Based on the serial number on the motor (1897016), this Mecury 500 is a 1966 model. Turns out its a better match to the boat than I realized. I had thought the motor would have dated to the 70's.

I'm thinking about stripping the paint down and repainting the motor. Does anyone know if original decals can be obtained if I do so?

Rob

I've found some reproduction decals, but interestingly enough the set that matches ( www.outboarddecals.com/popup_image.php?pID=2405&image=0 ) is the 1965 set.

Would Mercury have used up whatever decals they had left from the 1965 run on some of the first 66's? The serial number reference I found ( www.maxrules.com/models/Merc_model_files/40-50.html ) indicates that 1965 numbers ran from 1755549 to 1870388 and 1966 was 1870389 to 2097444. I wouldn't think that they would still be using the old year model stickers 29,000+ motors in.

I have a 1965 Merc (stripes are like yours). My father had 1966 motors (they had a more silver wide stripe with Mercury written inside). I can't speak for any past practices by a manufacturer...however, both your faceplate decal and side decals are 1965...is it possible someone swapped them?...to do both I would think not, but one never knows. I got my decals for my 1965 from
www.johnsmcintoshvintagemercuryoutboard.com/Decals.html

He is in Hayward, Wisconsin. I met him in person at the Tomahawk, Wi national antique outboard show. Great guy and he had my stuff (I even bought a nice shirt and sweatshirt with the old logos...he made my day!)

I will let the transom experts jump in for advice.

Dr. Go!

Rob, you're getting some good advice here. I would be a little concerned about the transom but the way you describe it there's a few good years left before you need to be concerned about replacing it, especially if you are just using it for trolling etc. Take a wrench to the inside of the transom and tighten up that "eye", put some silicone around the bolt first to seal it up from water incursion.
Now that being said... good thing you're just fishing in OR. If you were to troll in Hawyard, WI you would need a safer transom and bigger motor. Here's a snapshot of average size Muskie and Bluegill. We grow 'em big here in Wisconsin.

Another good source for paint and new stickers is Peter at nymarine.com. I bought both items for my 1963 Merc 850 and was more than pleased with what I got.
Bill

No way to know really if the decals could have been swapped out in the past. I bought this boat from a guy in 2008 and haven't had much time to work on it till now. I got the impression he had not had it long, had got it as a project boat and then had to move. As such, I have no idea where I'd contact him. As I am fairly sure he was aware the motor was shot when I bought it, I'd probably be better off not contacting him anyhow, I might not be nice

The decals are not in terribly good condition, so I had thought they were original however perhaps someone had changed them early on to match the year of the boat for some reason?

The serial number on the motor is on the mount, perhaps the mount is a replacement and the motor itself is actually a 65'? Would there be any other places on the motor with the serial number marked?

Thanks to everyone who has posted replies today. The helpful spirit I've found on this forum is wonderful. I've been on so many forums where questions languish for months before any responses come back. Its quite refreshing.

As this is all very new to me, I feel that I'm going to be a taker of information rather than a giver for quite a while. I do plan to start a project thread on the progress of the restoration work I do on the boat, so hopefully that can help pay back by letting other people starting out know what mistakes I make as I go along.

I likely won't be able to get started on much until after the holiday's. Until then, thanks again all!

Rob

Be sure to take a look under that research tab. Quite a few pictorials and literature on fiberglass work. I believe in there was where I was reading to take a small drill bit, go into the transom from the inside (careful not to go thru the outer fiberglass hull) in a few spot from edge to middle and see what the wood shavings look like. Dry and light or dark and wet.