Outboard sizing! Need help please
Kinda long. I have a 1993 21' Jetcraft Blue Water aluminum boat. It was an odd duck with a 300 hp Yamaha 454 and a volvo SX outdrive. Always ass heavy and would never really trim correctly. It was plenty fast and I still have no idea how fast it would have gone just needed more prop changes and fuel. Speed is not the main objective. It is basically like all of the other aluminum jet boats of the era only stern drive.
Well that is all history now. The 1300 pound pig is out and the welded extended transom is going on now. I want a safe, capable, and fuel efficient boat. Don't need to go 50mph in the Alaskan waters. Looking at Yamaha and Honda. Yamaha would be the easiest service at Rocky's only a ferry ride away. Usually fish within 5 miles of town(Coffman Cove) but I may run out over 20. I use the boat hard for one month a year then it sits.
How much horse power do you reccomend? I know big question but I need your thoughts and logic! I actually know a guy with the same set up and a Honda 150. Cruse is 25 at 3500-4000rpm 3.5 mpg with average weight and 5000+ with lots of weight. He is quite happy with his set up.
Thanks for your suggestions!
Before you can decide how much power you need you need to determine how much your boat will weigh with the motor and all the gear on it. You should take into consideration people, fuel, meat, fish, batteries etc.
Will you be running a prop or a jet? For prop use I would try to stay with a ratio of 1 hp per 25-30 pounds of "wet" boat weight.
For example if your rig weighs 5,000 pounds with everything I would consider a 175 at the low end and a 225 at the top.
I always go for a little bigger motor as it can be run at a slightly lower rpm than a smaller motor (and usually better fuel consumption) and it gives you some insurance if you need to carry more gear or make it back to port in a hurry.
Thanks Snowwolfe. I have no idea what the weight will be. I guess that I can look for some type of scale when I get it back.
How aouut a Honda BF200
My Honda dealer has a 225 for $15400 and a 200 for $13400. I am feling like $2000 is a bit much to pay for 25HP. I think that I wil average around 4K as far a weight goes.
One thing to think about is that an underpowered boat will use more fuel than a slightly overpowered boat. An out board that is too small will suck more fuel from beeing maxed out all the time than a motor that is a little bigger and being ran a litlle easier at lower rpm. Might lean towards a 175. just an idea here.
I am over in K-town and have a 21' Edwing, heavy aluminum, cabin. Not sure on weight. I have a 100hp Yamaha. I cruise at 18 knots, with a load. I have over1200 hours on it with no problems, except I feel I am under powered. I want to go with a Honda 150. Timber marine had some good deals not to long ago. I have bought outboards at Rocky's. Great people to deal with. I would give them a call and see what they think.
I went with the Honda BF200. A little more was better than not enough. I found out that the BF225 only produces the extra 25 hp over 4800 rpm. The torque does not change according to Honda. I will only see those RPMs when the water is perfect and I feel like having a little fun. I have attached a picture of my transom work so far.
Take a look at Yamaha's web site. They have quite a bit of performance data there on various boats and different motors on them. Maybe you can find something close to your's as far as the basic configuration and this will give you an idea of what manufactures are using on new boats of a similar size, as well as the fuel burn rate, best cruise speed, and top speed of the boat.
Last edited by jrogers; 02-03-2008 at 21:58.
Reason: spelling error
The boat manufacturers association recomends an ideal loading of 25# gross weight per hp, and a max loading of 40# per hp. I.e. you'll likely get the best performance at 25#/hp, and you'll still be able to plane at 40#/hp.
So figure out hull weight, fuel, fishing gear, passengers and engine weight, and divide by 25. Boats in the same length can very greatly by size.
There are hp ratings for hull length, and too heavy of an engine on the transom will mess up your trim. But asside from that issue, few people have problems with a bit too much power, many folks wished they'd gotten the next size larger engine.
Boats get heavier with age, and engines get weaker with age, also undersize motors that have to run near wot to cruise burn more fuel than a larger engine running about 2/3 max rpm.
No knowing your gross weight I'm guestimating your looking at 115 on the low end, and 175 on the high end. While honda makes a good reliable motor, they are typically heavy for a given hp, and IMHO overpriced by a few thousand. Yamaha has a solid reputation, and if you have a local dealer you might want to consider the Suzuki.