How fast should my motor go?

[NeWcS]

I have a 18hp Jonny seahorse18 and wanted to see how fast I should I expect to go. Its on a 14' alum v-hull. The most ive seen on the GPS is 16mph.<br /><br /><br />-Jay

 

[Chinewalker]

Re: How fast should my motor go?

Hi Jay,<br /> That's not too bad. Have you ever hooked up a tach to the motor to see if it's spinning max revs? It should top out at no more than 4500 revs with just you and a light load aboard. A little set-up and prop work might nudge it up a mile or two, particularly if your revs aren't up where they should be.<br />- Scott

 

[steelespike]

Re: How fast should my motor go?

Scott,It seems to me I read years ago in a Johnson catalog that the 10 was estimated to reach 21 mph stock under ideal conditions and the<br /> 18 was good for 27.We had a 61 18 on a wide 15 ft Chris Craft kit boat.It would hit 23 to 25 regularly and once touched the magic 27 ever so briefly.Of course the old speedos werent to accurate so Im sure there was some error there.<br />But my point is it would seem that a properly trimmed 14 aluminum with a healthy 18 would surely make 20+ mph dont you think?

 

[Paul Moir]

Re: How fast should my motor go?

It does depend on the boat a lot. Can you describe it a bit please beyond what you have there? Like how strong a V and approximate weight?<br />On a light utility hull (flat-bottomed tinny, probably no more than #200 on it's own) I can get around that with a 6hp outboard. 55Crestliner is getting near 25mph with his '57 18hp, but I think that's a flat-bottomed Al boat as well - and none too beamy!<br />But if you're pushing around a 1000lbs+ worth of ocean-going craft, maybe 16mph isn't far off. A tach will tell.

 

[cobra 3.0]

Re: How fast should my motor go?

What pitch prop do you have on? 16 is slow. Alone I get almost 30mph with a 15 Evinrude 2 stroke GPS on a light 14 foot aluminum cartopper. I used to have a 18 Merc on the same boat that did 31 mph(alone).

 

[Chinewalker]

Re: How fast should my motor go?

Hi Spike,<br /> I think the Johnson Catalog numbers were a bit on the "happy" side. I GPS'ed a '52 Merc Super 10 Hurricane on a 12-foot Dura-Nautic at about 28mph, which was really honkin'! The '48 Lightning 10 (KE7) would run about 23 on the same hull, and the intermediate KF7 Super 10 would runa bout 24. My K-10 Chris Craft Commander ran about 26, as did a Scott 16hp (same displacement as the Mercs and CC). My Fastwin 15 Evinrude ran about 24 on the same hull. My '56 Johnson 10, as nice a motor as it is, didn't come anywhere close to those, although I never ran that one with a speedo. My Dura-Nautic is a fairly light, wide, relatively flat bottom boat and handles up to 20-cubes with ease (see my Avitar). <br /> I did run a Mark 25 on the boat once, but had too little blade on it. That motor would stand the boat right on it's transom and be planing in less than 2 seconds, but would be screaming its guts out at wide open. It was kinda like dropping the clutch in a car that could get rubber in more than first gear. Someday I'll find a prop with bigger bite and try it again.<br /> Anyway, yes, a solid 18hp on a modest 14-footer should easily top 20mph with a light load. 16mph might be okay with a couple people, tanks of gas, the dog, cooler and fishing gear for the day. I should have asked for more info on the hull, load and setup...<br />- Scott

 

[NeWcS]

Re: How fast should my motor go?

Thank you all for the replys.<br /><br />-Jay

 

[55Crestliner]

Re: How fast should my motor go?

I'd also be interested to know how much your boat weighs, what design it has, and what prop you're using.