Capt. Rob wrote:
The engine is predicted to need 65 HP to make hull speed.
I have 10 extra HP.

Bart, I'm no expert on engines, but that seems underpowered. I thought
hull speed should occur within 60-70% of rated horsepower in calm
conditions. For example....and my math is admittedly fuzzy here....the
35s5 makes hull speed with 16.6 HP on her 28 HP Volvo diesel. With your
vessel's weight and wetted surface ratio, 10 extra HP seems way to low.

Jeff has it right in his post. The number is around 65 HP.
He is probably more accurate as I was going by rough
numbers with his number of 64. I believe I used it method
and just rounded it off when picking an engine. There is
not perfectly accurate method. 1-2 HP either was in ot a
big deal. One thing you do not want to do is pick too
small an engine.

YOur boat has an extra 11 HP to play around with. That
is good for you as you can add a HD Alterntaor or other
accessory and still drive your boat to hull speed.

The other thing is the prop. It should be designed for the
type and weight of boat at the engines max rpm. I relied
on Chuck at Flexifold for this information. He was a big
help.


A 46 foot J Boat carries a 76 HP engine, but doesn't it weigh a lot
less than your boat? I thought I saw an Ercison 46 for sale some years
back and it had more like 105 HP.

Most boats in this size range us the Yanmar 75 HP engine.
The trend in recent years is to up the size of the engine
slightly over the sized used 20-30 years ago.

The J-44 I've seen has a 55 HP engine. That is a lot lighter.
I would have prefered a naturally aspirated engine lilke that as
I feel they are a bit more reliable. The J-46 is about 24400 lbs
--heavier than a J-44 at 20500 lbs, but not as heavy as my
31,500 lbs.

I can only guess that the J-46 has many engine driven
extras like a water maker, I read it has a "hard to turn" 140 Amp
HD alternators, and perhaps engine driven refridgeration. All of
which require substantial HP to service. It probably carries more
water and fuel and being a cruiser is likely to be loaded still
heavier which would bring it's weight up closer to mine.

My boat is a beastie weight wise--that is both good and bad. The
J-46 with the same engine, is surely propped differently and I'm
sure it will be more economical to motor. Weight is the single
biggest factor in fuel economy for diesel powered vessels. If my
wieght starts to climb, I'll be glad to have a bit more HP and the
option to change my prop size and pitch.

I can't imagine an Ericson 46 having a 105 HP engine unless it
was added by an owner who didn't have the sense to calc out the
correct size. I could have easily put a 110 HP more in ECHO--the
footprint is the same, the cost is very close, but the extra HP
would be consuming fuel I didn't need. More power is only
good on planing hulls like powerboats.