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I'm just curious. Several times on the forum I've read that a 15' is faster than a 13' with the same power on it. I never did believe that from a purely theoritical standpoint. The weight difference and the hull shape are my big nay sayers.
This weekend we had a chance to compare, but with different engines. My son was in my 1968 13 with Nissan tldi 40 hp with 13" SS prop. A friend was in his maybe 1982 15' super sport with same vintage Merc 60 hp. I don't know what prop he has, but for this comparison it shouldn't matter. Both had two on board and were returning from fishing. They wre cruising along and decided to test the theory. Both accelerated to wot. The 15' was turning 5400 rpms, his usual max rpm, and my 13' was turning 5600 fully trimmed out. 41 mph on the 13' easily walked away from the 15'er, and I stress easily. My friend just sat there bug eyed and in awe. He couldn't spell fast with enough a's to describe it.
Tell me what I'm missing.
Mike

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HI MOOSE, Maybe a sack of crawfish!!
Whalerman

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Moose, sounds correct on the speed . I have a 15 cc w/98 70hp Evinrude top speed is at 40mph. One person and 3 gallons of gas. BG

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My friend has a 1969 sport 13 w/ the "Merc" 4 cyl. 40 H.P. (early 90's I think) on it. I have the sport 15 (w/ a "Rude" 48 SPL on it at the time) and we would often race on the Bay. If it was flat calm the sport 13 would easily walk away from me. In the "Chop" though, I would easily pull away from the sport 13, I think (I.M.O) it had to do more with the "Hull" design difference on the sport 15 than engine H.P. when over taking the sport 13

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Maybe the "vintage" Merc 60 is a little tired. Might not be putting out a true 60 hp anymore.

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To really know, do the test run again only this time twice (2 round trips). Same number of gals. fuel,same or as close as possible, wieght in both boats. If you still walk away from the 15er, then the 60 merc maybe alittle tired. Also are the boats kept in the water?

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The Merc 60 just got a new trigger and a tune and runs great. It hits top rpm at wot, so it's good to go.
Mike

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I have never heard that a 15 footer with the same power as a 13 will be faster than the 13, and I have heard quite a bit about Whalers over the years.

I have heard that about the 11 and the 13 from one particular source who has repeated it over and over.

In this case it seems irrelevant. Two different boats, two different motors, two different propellers, two different riggings, two different speeds. Where's the mystery?

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Like Tom is saying, in order to test the hulls, the hulls should be the only variable.

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The 15'' may not have the outboard mounted high enough nor the right pitchrd prop.

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Where are the guys that say a 15 is faster than a 13 with the same power?

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Stock 13 hull has a BIG hook, keeps the bow, speed, down. Take it out, you can air it out till it starts walking. MartyD

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I can trim it up so the hook is a non issue and it flies. Too dangerous to do for long.

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My 16SL with a 90TLR does 40 at 5200. It must be scary on a 13...

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I don't believe a 15 out runs a 13 with the same power on it. I once had a an 1980 15SS with a 70 Evvy looper, trimmed up it was a fast chinewalking boat or so I thought. I was out run one day by a 15 year old kid in a 67 13 with a late 80's 40 Evvy looper. The conditions were flat calm and we were doing 46 and 48 mph respectively. Afterwards the kid admitted that he faired the hook out of the bottom of his boat. The kids' boat absolutely hauled and he knew how to drive it well. (I'm going to guess that the kid also made a lot of money challenging old fogies like me to race) Another local '68 13 with a 500 M Merc (50 hp) runs at about 53 mph with no bottom mods.
Someone who understands how to set up and drive an old 13 properly can make them really fly. Almost hydroplane like. The 15 is deeper and heavier and in my book it's just not possible that a 15 can keep up with the little guys with the same power on it.

FF