ranger58sb
Guru
I have a Bullfrog 10'. The placard says 15 hp max. Bullfrog sells a version with a steering station and seat, the placard on it says 20 hp max. I enquired, they said the boats are identical, but the CG allows them to put a 20 hp placard on a boat with a wheel and seat. The steering wheel and seat can be installed or deinstalled with a couple of bolts.
I think remote steering is significant because it moves the weight of the driver to the center of the boat.
Weight mid-ship is the difference and all recorded as part of their testing.
If you remove the weight, then you need to move to the lower HP.
If you don't then, you reconfigured the product they sold you, without reconfiguring the max hp. So now down to you.
Yes - agreed. The rating is made based upon the stability of the boat and the loading with standard and max load. When the steering station is moved fwd the load is moved as well.
Our Walker Bay Genesis comes in two versions, too, one tiller and 15-hp max, one wheel and 20-hp max.
WB told us it was about increased weight, different placement of load, etc... as others have said.
Thought I heard (or read) at some point that difference in HP rating for the steering station vs. tiller configuration is due to the inherent instability on a shorter platform should one lose grip on the tiller at higher throttle settings...
Could be, especially given many are sitting on the tubes with a tiller-steered dinghy... but "inside" at a console. OTOH, WB's story was all about load weight and load placement.
What is interesting to me is the negligible motor weight difference. Recently bought a new Suzuki outboard for my dinghy. With in the same model class they have 9.9, 15, and 20 HP. They all weigh the same when configured in the same way. Only difference is top end RPM as limited by the engine computer. So in essence, if you run the 20 HP at 300 or 400 RPM off wide open, you have a 15 HP, same weight, same RPM. Other than the engine decals, there's no apparent difference at that RPM.
Used to be different, in that 10/15-hp 2-stroke motors were built on a shared platform, 20/25-hp outboards on a larger shared platform, etc...
But more recently 8/10-hp, 15/20-hp and 25/30-hp outboards have shared their respective platforms...
Suzuki adding their 9.9 to the 15/20-hp platform seemed a bit odd, to me...
Anyway, yes, running the 20-hp version at the same RPMs of a 15 would seem easily possible, but I'd guess it's not difficult to exceed those RPMs even if by "accident"...
But then I'd also guess all the cited downsides to "over-powering" would still apply if something happened to cause deeper investigation.
-Chris