Advice on new boat buy please/ underpropped?

[Turtle Blues]

Yes Sir,
Rechecked to make sure I didn't transpose them.

 

[Portage_Bay]

I would take what that owner says with a large grain of salt.

owner claimed 2.5gph total at 7 knots.

which is 2.8 nautical miles per gallon. Maybe at just above idle, maybe. My experience with the hull form in your pics for a boat of that size and weight is limited to two boats. But I expect that to get to 7.5 - 8.0 kts will be closer to 1.0 - 1.2 nmpg.

 

[DavidM]

That is a little strange, but technically, I don’t see why not.

David

 

[Turtle Blues]

Yeah, I' not real good at close monitoring, my fuel consumption calculation for slow cruising is 1npg.

 

[rslifkin]

I would take what that owner says with a large grain of salt.

which is 2.8 nautical miles per gallon. Maybe at just above idle, maybe. My experience with the hull form in your pics for a boat of that size and weight is limited to two boats. But I expect that to get to 7.5 - 8.0 kts will be closer to 1.0 - 1.2 nmpg.

2.5+ nmpg at 7 kts is not unreasonable for a 41 footer. Above 7 it'll go down fast. At 6.5 - 7 kts I'm over 1 nmpg with gassers, diesels will do much better than lightly loaded large gas engines.

 

[O C Diver]

As a point of reference, Slow Hand (50' LOA, 42' WLL, 40K to 45K displacement) cruised:

6 knots 1.2 GPH 5 MPG
7 knots 2.0 GPH 3.5 MPG
8 knots 3.7 GPH 2.1 MPG

Single 4045 John Deere @ 135 HP
2.5:1 ZF gear
28 x 20 4 blade Michigan propeller

Ted

 

[Turtle Blues]

Ted,
Your numbers bring tears to my eyes. It makes extended cruising look affordable.

 

[O C Diver]

Ted,
Your numbers bring tears to my eyes. It makes extended cruising look affordable.

When fuel was over $6 per gallon, I did a lot of cruising at 6 to 6.5 knots. Nice to have a 3,000 mile range and tanker at $3.47 instead of $7.00 per gallon.

Ted

 

[Portage_Bay]

As a point of reference, Slow Hand (50' LOA, 42' WLL, 40K to 45K displacement) cruised:

6 knots 1.2 GPH 5 MPG
7 knots 2.0 GPH 3.5 MPG
8 knots 3.7 GPH 2.1 MPG

Single 4045 John Deere @ 135 HP
2.5:1 ZF gear
28 x 20 4 blade Michigan propeller

Ted

Wow! Remarkable efficiency. Wish I could see numbers like that.