Engine selection and swap for larger

HoratioHB

Recruit
Joined
Jul 24, 2007
Messages
4
Hope I didn't miscategorize this, but I really couldn't find anything that looked any better than this thread.

I just bought a '65 Arkansas Traveler Atlas 16', came with a 40hp Johnson Seahorse built in 1966. This motor seems to be flawless with the lower unit being rebuilt less than 30 hours ago, however I my knowledge is very limited on boat engines.

I am thinking of buying a 60hp Johnson Seahorse to replace my 40hp Johnson. My main use with the boat will be fishing on the Columbia River in the Portland, Oregon area with some local lake fishing as well. I would like to occasionaly, during the summer months of course, to pull my wife and son (toddler) out on some tubes and other towed vehicles, or whatever you call those things nowadays. Not planning on any waterskiiing, but some wakeboarding "might" come up eventually during summer months as well. The 60hp also has the added benefit of an alternator on it so I can buy some electonics to put on the boat.

My question, what kind of speed/performance difference would I find between a 40hp and 60hp on a 16' boat. I don't have any pictures, but there is a boat just like mine at:

antiqueboat.com/boats/MoreInfo.asp?SKU=cole16

Not sure if that helps, but as I said I don't know much about boat motors and would assume the hull style might make a difference.

I read somewhere else in these forums today that the gas useage is roughly:

HP / 10% = gallons per hour

Is that about right?

Final question, if I bought the 60hp, would I want to take the prop off my current 40hp and swap? The reason I ask that is because the previous owner made it very clear that he was getting best gas mileage and performance for what he used if for (fishing only) from the prop that was on it now and he also said that he tried several different props before settling on that one.

Thanks!
 
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tashasdaddy

Honorary Moderator Emeritus
Joined
Nov 11, 2005
Messages
51,019
Re: Engine selection and swap for larger

on that boat i would actually look for a 70 hp. also make sure you are not carrying any unwanted weight, such as water saturated foam, under the floor. you will have to decide on the prop after mounting the motor. on the 70 you want the motor turning around 5000-5500 rpms, at wot. this is what you shoot for when propping the motor. and correct engine height in relation to the bottom of the boat. you don't have to use all the power, but as that toddler gets older he/she is going to want to take friends, and then the load gets heavier.
 

steelespike

Supreme Mariner
Joined
Apr 26, 2002
Messages
19,069
Re: Engine selection and swap for larger

What ever motor you get be sure the shaft length is right.
Short shaft is approximately 15 inches,long shaft is approximately 20 inches.
GPH(gallons per hour) is roughly 10% of hp. ie: 70 hp = 7 gph at wot(wide open throttle)
 
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