Top speed of 22mph question

[philobite]

I've a question regarding the top speed of my '68 Larson Volero 177 ('17) with an '87 Evinrude 48 SPL. FYI, you can check out the Larson Volero here (go to pg 14). It's a fairly deep "V".<br /><br />With just me in the boat the top speed (GPS) I've attained is around 21-22mph.<br /><br />My question is: does this seem the right top speed for this engine/boat combo or should I be getting a bit more out of her?<br /><br />Details:<br />- Hull is stripped of furniture/cabinetry. There are only two light single-post chairs forward.<br />- 2 marine batteries in rear bilge area, 2 batts forward.<br />- 18 Gal fuel tank fwd in bow (full).<br /><br />- Prop is 12.25x15 garden variety aluminum with a few nicks filed out of it.<br />- Cav plate is even with bottom of hull, and about 7" behind transom.<br /><br />I don't have a tach. I can tell you it "feels" to me like I'm not running at top RPM, but rather lugging a bit.<br /><br />Any thoughts, advice (or questions)?

 

[wileecoyote985]

Re: Top speed of 22mph question

philo<br /><br />What is the max HP your boat is rated for? I'd think you are severely under powered with a 48 HP on that hull.

 

[Texasmark]

Re: Top speed of 22mph question

Agree with wilee. Speed seems appropriate for engine size.....you are just barely getting on plane. Once you get over that hump (with higher hp) you will notice a disproportionate increase in speed for a given hp......reason is prop slip. The faster you go, the less boat in the water, the less resistance and the less prop slip. My boat runs about 35% slip at 25 (3600 rpm's) to 8% at 50 (5600 rpm's).<br /><br />Mark

 

[philobite]

Re: Top speed of 22mph question

Thanks for the replies. I'm not sure what the max HP for the boat is (there is no placard on the hull), but probably 100-120 range.<br /><br />Texasmark, that's good info. Thanks for the specifics as it helps me learn.<br /><br />The boat and motor were a gift to me and it's not financially in the cards to get a larger engine anytime soon. Understanding that 50hp is indeed underpowered, I'm wondering if a change in prop to 12.5x13 might reduce prop slip and squeeze a bit more out.

 

[cougar1985]

Re: Top speed of 22mph question

maybe 13p would help a tad.had a 60 mariner that a guy was running on a 19foot glass fishing trawler and it was 11p.

 

[Texasmark]

Re: Top speed of 22mph question

What I'd do is live with what you have and when you can afford it, get yourself what you want. Otherwise you are just feeding a sink hole for money. Grin.<br /><br />Mark

 

[philobite]

Re: Top speed of 22mph question

Thanks all for your help. Looks like I'll enjoy what I have for what it does well (fishing and light recreation for our children - tubing, etc), and give up the morning coffee and put the savings from that in a can for a 70-90hp down the road.

 

[Rancherlee]

Re: Top speed of 22mph question

I've got a 16' aluminum vee hull fishing boat with close to the same engine (55hp johnson twin cylinder) and with a 12.25x15 prop I'm turning 5300-5400 WOT which is just under the 5500rpm rated HP spec and I top out at 29-30mph with 2 people and 250# worth of fuel/fishing gear/batteries in the boat. I Think a 12.5x13 would work great on your boat, I'm going to be picking one up soon for mine to pull a tube with.