Horse Power at the prop

[NC22]

I have a 1969 25hp Johnson motor and I was wondering if anyone could tell me what the HP at the prop would be? Also I have a 1981 16 foot Lund with the info plate telling me that the hp max rating is 25hp(this is tiller driven). For this year of motor I'm assuming this means at the powerhead. Am I assuming correct? When did motors start rating at the prop? I would like to upgrade this motor and am wondering what to look for. I would like to get the max hp for this boat. Sorry there are so many questions. Thanks to anyone who can help.

 

[roscoe]

Re: Horse Power at the prop

Welcome to iboats.<br />The diference is insignificant. Just a couple of hp, if that.<br /><br />Put a 25 on it and go boating.

 

[DJ]

Re: Horse Power at the prop

10%, difference, on the outside. For you, that equates to 2.5 HP.<br /><br />Like roscoe said, clamp on the 25 and go. Great engine, by the way.<br /><br />Domestic outboard makers started "prop. rating" in 1983.

 

[NC22]

Re: Horse Power at the prop

Thanks alot for the info. I was told at the dealer by a mechanic that the hp would be equivalent to a modern 15 hp (at the prop) motor. It sounded like too much of a differance to me, so I thought I would ask here. Thanks again.

 

[dajohnson53]

Re: Horse Power at the prop

The only thing I could think of is that if the '69 is getting worn, it might not perform as well as a modern engine of similar (e.g. 20 - 25) HP. There's also a weight issue - the 15 HP your dealer was talking about could be quite a bit lighter, and that combined with a tired '69 might add up to a new 15 giving you similar over all performance. However, my guess is that, unless your 25 it is really worn, a current 15 wouldn't be close. <br /><br />How does the '69 run? How's the compression.<br /><br />Final comment: I always come down on the side that a guy should get close to the max. HP for the hull, if it is affordable. I would be very hesitant to replace the 25 with newer 15. I'd definitely go with a newer, used or rebuilt, 25 before I'd go with a 15, if that's all I could afford (which is generally the case - I have a '74 kicker and an '82 main!).

 

[NC22]

Re: Horse Power at the prop

I am not sure of the compression. I bought the boat over the winter from a dealer and the only thing I have done to it was to replace the plugs. It did turn over good and start on the 3rd pull so it seems to be in good starting shape. I also put it into the river to see if the water pump was working and it was spitting out water so that seems to be working also. I will have to get it on a lake and see what the top end is like. Thanks for the replys.

 

[River - Runner]

Re: Horse Power at the prop

nutcup22 - Keep that motor! I bought my 1969 Johnson 25 new and still use it a lot. It is very light for it's power - 78 lbs. Only repair ever was a set of plugs, points and condenser. I do after using it pull the rope slowly a couple of times as to not start it. This drains the water out of the lower unit. The motor always holds a little water in there. It is a very good motor and I would regret ever parting with it.

 

[NC22]

Re: Horse Power at the prop

Thanks for the info guys. I have no intentions of getting rid of the motor. I was just wondering if a newer model 25 would give me more speed. I am a firm beleiver in keeping items for rainy days. " PACKRATTING " Thanks for the water pump info river-runner. I am curious as to the pitch of your prop. I do not have a tach. and currantly there is a 9 x 9 on it. I have purchased a 9 x 10 for it. Either as a main prop or a backup. Depends which one works better for top end speed. The lake I like to fish is 9 miles long, and I usually fish the whole lake when I am fishing it.

 

[DJ]

Re: Horse Power at the prop

If you're not sure about the rpm, you may want to look into one of these.<br /><br /> http://www.tinytach.com/

 

[River - Runner]

Re: Horse Power at the prop

My 1969 Johnson 25 has the original prop that came with the motor. It's a 9 x 10. I do not have a tachometer for this motor but it seems fine to me. The motor is run on my 1968 FD Alumacraft and it will really scoot. Boat is 14 ft, beam is 4' 5" and boat only weighs 160 lbs.<br /><br />Here is a picture of the boat, but it has my 40 hp motor on. I do not have a picture with the 25 hp motor.<br /><br />

 

[dajohnson53]

Re: Horse Power at the prop

Beautiful picture - makes me homesick for MN in the fall. Also, I'd like to see that AlumaCraft moving with the 40 merc at WOT, jumping some wakes!

 

[NC22]

Re: Horse Power at the prop

Very nice picture River-Runner. Looks a bit over powered though. I bet it gives one wild ride. What is the alumacraft rated for as far as hp max? My lund is 16' in length and 5'5" width, and is only rated for a 25horse. Is this rating mainly for manuverability at WOT, or a combination of motor weight and handling? It just seems to me that if your 14 footer can handle a 40, then mine should be able to also. As long as I am carefull with it and respect the extra power.<br /> Thanks for the info on the tinytach DJ.

 

[River - Runner]

Re: Horse Power at the prop

nutcup22 - Click on my folder icon and then click on View Recent Posts (on top to the right). I do not have many posts but read what is of interest or pertains to you. This is important stuff!<br /><br />Think safety first!