'57 Johnson 18 Top Speed

[55Crestliner]

I finally brought a GPS in my 12 foot Crestliner with '57 Johnson 18 horse. My dad and I both weigh about 245, and my boys are about 40 each. With all 4 of us, the boat does 20.4. Then I went out by myself, and the boat did 22.8. I would have assumed there would be a bigger difference in speed without that extra 325 pounds. <br />Is this telling me anything about the prop I have? I'm guessing it says the prop is correct, but I don't know. Any thoughts?<br /><br />Is 20-22 about right for this setup?

 

[cajun555]

Re: '57 Johnson 18 Top Speed

55, Really the only way to know if your proped out right is with a tach. I believe on that motor wot rpm is 4000. I just got a tach from www.tinytach.com. Simple to hook up and takes the guess work out of trying to buy the right prop. Also a spare prop is not a bad idea. My spare sure saved my butt this weekend.

 

[55Crestliner]

Re: '57 Johnson 18 Top Speed

Would this motor take a 1C or a 2C? I emailed Tinytach, but never got a response.<br /><br />I'm a little bothered that they say the battery is NOT replaceable, but I guess for the price it's not too bad.

 

[roscoe]

Re: '57 Johnson 18 Top Speed

They have an 800 number on their site.<br />I would call them to place the order.

 

[Paul Moir]

Re: '57 Johnson 18 Top Speed

You want the 2C.<br /><br />One Iboats member recently accidently bought a 1C instead of a 2C, but found that by wrapping the pickup around both spark plug leads it would read properly instead of 1/2 RPMS.<br /><br />It's too bad about the battery - I think the 'commercial' ones take an external power source. Better call and get details about it though.

 

[55Crestliner]

Re: '57 Johnson 18 Top Speed

2C - thanks!

 

[petrolhead]

Re: '57 Johnson 18 Top Speed

I wonder what makes the battery non-replaceable? If they put a battery in there in the first place, surely it can be taken out and a new one installed, it may mean cutting the unit open and a bit of soldering but that's no great problem.

 

[cajun555]

Re: '57 Johnson 18 Top Speed

55, I e-mailed them, they recommeded the 2xL for my 56 30 HP, which is basicaly the same motor you have.<br /><br />As far as battery replacement the unit is sealed and supposed to be water proof but I guess with enuff silicone any thing can be water proof.<br /><br />IMHO, a tach is probally the single most important instrument you can have on your motor. I thought I had been lugging my motor down but infact at wot my rpm was 4380. <br /><br />I spun a hub the other day so I picked up a new prop and went up 1 in. Now rpm at wot is 4020 and also picked up 2 to 3 mph.

 

[55Crestliner]

Re: '57 Johnson 18 Top Speed

Not seeing the 2xl. Is that a typo? Or different section than this page?<br /><br /> Tinytach gas tach page

 

[cajun555]

Re: '57 Johnson 18 Top Speed

55, just found invoice. P# TT226R-2XLR. When I ordered my tach I called the company and confirmed with the sales rep. of what my application was going on. This unit also has resetable hour meter. The only mistake I made was I wish I would have ordered the wire to the lenght I needed. I just stayed with the standard 6 ft lenght, thinking of using only temporary on my main motor, but thats ok, I can mount on cowling somewhere. <br /><br /> Good Luck

 

[petrolhead]

Re: '57 Johnson 18 Top Speed

Does anyone know of a reasonable priced tach with a linear readout rather than digital? Preferably one that works in the same way as the tiny tach, ie an "antenna" wire that just wraps around the HT lead.<br />A digital tach just looks a bit modern for my 50s style boat, and I don't really want to get involved with any complicated wiring, am I asking too much?

 

[55Crestliner]

Re: '57 Johnson 18 Top Speed

Originally posted by petrolhead:<br /> Does anyone know of a reasonable priced tach with a linear readout rather than digital? Preferably one that works in the same way as the tiny tach, ie an "antenna" wire that just wraps around the HT lead.<br />A digital tach just looks a bit modern for my 50s style boat, and I don't really want to get involved with any complicated wiring, am I asking too much?

That's Exactly how I feel, would love to have a dial.

 

[mjbrueck]

Re: '57 Johnson 18 Top Speed

I've got a similar set up with my '57 18hp Johnson. Mine is on a 12' homebuilt boat (about 125# hull weight). Solo I'd go 25mph at WOT. I got a TinyTach and found out that at 4500rpm (max rpm for this motor), I would go 22 mph. No more solo WOT.<br /><br />I've got the 9-1/4x11 prop on mine. Mine will only do about 14mph with two adults, two kids and gear (about 800# total displacement). I've also found that the other props available for the motor don't help when you're loaded heavily. The 9x10 will do about 17mph solo and 11mph with the above weight. The rpms are higher but it won't fully plane. With the 9x9, I get 11mph solo and 11mph fully loaded.

 

[55Crestliner]

Re: '57 Johnson 18 Top Speed

Well mjbrueck, you have just gotten me more confused. I don't understand how your 9x9 will only get you to 11mph solo, but my 9x9 is doing 22.8 solo!<br /><br />I have a friend at work that told me his deep V 13 foot fishing boat with a 15 horsemodern 4 stroke will go 26 by himself. I know my boat doesn't weigh much more, if at all, than his boat.<br /><br />Am I still missing something here?<br />"Solo I'd go 25mph at WOT" - It just doesn't make any sense that a 9x9 would be THAT much slower than your 9-1/4x11.<br /><br /> <br /><br />I know, I NEED a tach.

 

[mjbrueck]

Re: '57 Johnson 18 Top Speed

I assume it's slipping a lot more than the 9-1/4x11. I originally had a 9x10 and a 9-1/4x11 when I got the motor. The 9x10 prop didn't feel "right" when the boat was loaded. It would rev up, but it wouldn't fully plane. (My boat is fully on plane at around 13 mph.)<br /><br />The 9-1/4 was a bit dinged up, so I got two new props from Propco - a 9-1/4x11 and a 9x9. I don't know if there's a way to equate different diameters to estimating speeds (I know larger diameters are more efficient), but a 9 pitch vs an 11 pitch should give 18mph with the same slippage(vs 22mph, 25mph was above 4500rpm prior to getting the tach). With the 9x9 and 9x10 there's a lot more throttle left, but the rpms are at 4500.<br /><br />Are you sure you have a 9x9 on yours? I think the 9-1/4x11 was standard and the 9x9 was for heavy loads - don't know how common they were.

 

[55Crestliner]

Re: '57 Johnson 18 Top Speed

Yep, 9x9. I bought it new.<br />I also have a 9 1/4 x 7, haven't tried it yet, and a 9 1/4 x 13 twin blade, seems slow - too much prop, and a 9 1/4 x 11, but it is so badly banged up, I didn't want to use it as is.<br /><br />I'll just get a tach soon and see what's going on.

 

[McGR]

Re: '57 Johnson 18 Top Speed

Your speed sounds about right to me. I used to have a '69 Johnson 25hp on a Sylvan aluminum fishing boat. This 25 was a somewhat more modern version of your motor with a few extra ponies. Based on your pictures, I would guess my boat was a little larger and heavier than what you are running. So, overall I had a few more horses and a little more boat... Nonetheless, the speeds you are getting are almost identical to what I used to get with this rig.

 

[mjbrueck]

Re: '57 Johnson 18 Top Speed

I guess not all props are created equal. I'm sure the Propco 9-1/4 x 11 is the same size/pitch as the original 9-1/4 I have, and the 9x9 looks right in pitch (I'm pretty sure it's not a 9x7). Propco doesn't put the size and pitch on the props, they're ID'ed as F9 and F10.<br /><br />Until you get the tach be careful with your top end. For me with the 9-1/4, the 25 mph would equate to about 5100 rpm. <br /><br />Also, I went in the garage to recheck my props and the one I reported as 9x10 is actually 9x10-1/2. It's an older prop and it's poor performance may be related to it being filed down to hide the dings?

 

[55Crestliner]

Re: '57 Johnson 18 Top Speed

Originally posted by McGR:<br /> ... Nonetheless, the speeds you are getting are almost identical to what I used to get with this rig.

That's good to hear. I wasn't trying to have the fastest boat around, or set records, (I'm not dillusional, that'll never happen ), I just wanted to get an idea of whether I have a real dog, or a hotrod, or somewhere inbetween. From what I'm hearing, sounds like it's just fine, wich is fine with me.<br />20-22 is pretty exhilerating on a 12 footer, I think.<br /> <br />As a side note, I had a 9-1/4x11, my neighbor had it on his early 60's 18 that he gave me. It was in real bad shape, pretty dinged up. I decided to work on it a bit. I set up a very simple jig. It was a piece of plywood with a hole drilled in the face of it, and a wood dowl that fit the prop shaft hole real snug. I placed this on my disc sander, and, using several different positions, I would rotate each blade into the sander. It came out real nice, but of course with a smaller diameter. I put it on the motor to find that the hub inside appeared to be set too far forward, meaning the prop was set too far back. Not much room for the nut, and there was a 5/16 gap between the prop and the lower unit.<br /><br />SOOO, I put it in my hydraulic press, it didn't budge - I did it again, and it split the prop wide open. Now it's in the trash <br />It's a bummer, I was anxious to try it out. Maybe after I get a tach (I just ordered one ) I can see if I need a bigger prop, and perhaps I'll find a good one.

 

[55Crestliner]

Re: '57 Johnson 18 Top Speed

I went out again last night, and got a little education. This time I had my boys with me for all tests, so that added about 90 pounds more than solo. <br /><br />I sat in the back, and saw a top speed of 24.9mph. That was after I adjusted the trim out to the last setting. That's a full 2mph more, with 90 pounds more weight! <br /><br />Then I sat in the front, with the boys with me, and it would only go 20mph - no more. It's rather obvious why alot of the old boats had the steering in the back, (like my Feathercraft) I had no idea it was that much of a difference. I think if I had known that, I may have put the wheel in the back, since I prety much built all the insides anyway. Oh well. <br /><br />There is another variable that may have contributed to these figures, I installed some home made "Feathercraft style" trim tabs as an experiment. All they are is 2 inch angle aluminum, 8 inches long, glued temporarily to the bottom outer edges of the transom. I really don't know if they helped or hurt, I think I'll yank them off and do the testing again with the boys with me to make it more scientific. I actually think they are just too small to really affect it at lower speeds like what they're supposed to. If after testing they proove to have helped, or not hurt, I think I'll put them on with rivets and call it good. <br /><br />I'm feeling a lot better now, I'm convinced I have the motor running real good, I just wont' be affraid to have a bit of extra weight in the back <br />