Comment by jcgrillo
6 days ago
Do you have any more information/sources to share on this? I have an Eastern 18 powered with a Yamaha 60hp 4 stroke and I've been struggling to dial the prop right. I don't know off the top of my head what the specs of my current prop are but basically I feel like I'm not taking advantage of the engine's torque at less than WOT, so I basically just run it flat out. If I could extract just a little more thrust out of the prop at lower RPMs it feels like the engine would have enough grunt to make the boat plane in the mid-high 4000s instead of 5000-5200rpm where I currently run it. Ideally, given the bsfc/hp curves, I'd like to run the engine at a bit lower RPM, but the way it's currently set up at ~4600rpm it's not fully up on the step. I was (perhaps wishfully) thinking a little more efficient prop design might help.
The other thing I was thinking of trying is swapping in a different "high torque" lower unit with a lower gear ratio and running a significantly larger prop.
Sources are primarily boating forums, dockside conversations, etc.
In theory your boat in right in the sweet spot of recommended power range at 60HP. I don't know all the background on it, so all kinds of potential problems, but I would wager that "propped wrong" is unlikely to be the core culprit.
I'd start by getting it weighed and comparing your loaded weight to manufacturer specs. USCG requires positive buoyancy for hulls under 20'. This is typically achieved with using expanding foam in hull cavities, and that foam can have a tendency to absorb and hold water if the boat develops any failure of the seals around the bilge areas that are foamed. Reports of poor performance are very common for these sub 20' hulls because of waterlogging. If not a waterlogged hull, you might also just have too much stuff on-board.
To a lesser degree, a bimini can also have an adverse affect on speed/planing, if it's acting like a parachute. Not sure if you have a bimini, but if so it's worth trying a run with it up vs. down.
I'd also look at how your outboard is mounted. It's not clear if it the outboard from the factory, or if the boat has been repowered. Outboards being too high, too low, etc. are pretty common issues that can also majorly impact performance.
That's a few thoughts that comes to mind off-hand.
Yeah, you're likely right it probably makes sense to just run it rather than trying to optimize further. As for excess weight, there is some--mine is a rare variant that has a small cuddy cabin forward, and that thing is really wet and needs to be completely rebuilt. A previous owner's refit of the decks removed any flotation there may have been originally, but also introduced a lot of unsealed wood which is now wet and heavy. It needs a deck job soon.
The boat was re-powered under my ownership. I'm pretty confident the motor height is correct based on a variety of observations and measurements, so I don't think there's really anything to adjust there.
I wouldn't say I have a complaint with the boat's performance, more like trying to get the engine to run at cruise in a more efficient range of the bsfc/hp map, which may be a tall order at 60hp. To your point, though, if I can shed a couple hundred pounds in the refit that could very well do it.