Is this speed realistic

[tiltrider1]

I’ve seen 16kts on the GPS & 10kts on the log. That doesn’t give me a cruising speed of 16 kts. It means Mother Nature is giving me a free ride.

 

[OldDan1943]

I’ve seen 16kts on the GPS & 10kts on the log. That doesn’t give me a cruising speed of 16 kts. It means Mother Nature is giving me a free ride.

Oh yea especially in the Gulf Stream, going north
Heading south, stay within a couple miles off shore to avoid the Gulf Stream effect.
Once in the Gulf Stream, going north, you can use it to your advantage. Speed I guess, if you are in a big hurry or extending your fuel range or, ‘saving’ your engine.
Of course, heading south, stay close to shore or inside the ICW.

 

[rslifkin]

Good post rslifkin but it’s not how far we go but how much meaningful experience we had. A good row on a lake in the morning and dinner in the camp nearby. Most here think you’re gonna have more fun in a bigger boat w all the bells & whistles.

Agreed, and that's why we don't mind the times where we can't go far. But being able to reach farther means we get to see more places instead of going to the same few places a bunch of times.

 

[T210DRVR]

I run at 1600 RPM and see +/- 7.6 knots with a clean bottom. I plan for that speed because the engines seem happiest there. The boat will do a bit over 8 knots WOT but mostly I get a lot of noise and higher fuel burn running her that way. She’s an old girl at 47 years old so I don’t ask too much of her.

 

[Nomad Willy]

Agreed, and that's why we don't mind the times where we can't go far. But being able to reach farther means we get to see more places instead of going to the same few places a bunch of times.

rslifkin,
Yes I’m in a rut but I still enjoy the drive to the boat. Liked it better when Starbucks was open. But that’s at 60mph. Doing an 8hr run over and over again at 6 knots in the boat gets old. To me cruising is about the trip .. not so much the destination.
But so many boaters run hard for days upon days to get to SE Alaska to see what the’ve heard is there. But it’s twice as far back.

 

[Nomad Willy]

Baker and Codger,
Re yesterday I agree w you both. And you two aren’t the standard of normal either .. you’re both special and thank the man for different.
I did go astray yesterday and thanks for put’in up w me.

 

[Swfla]

SOG and SOW is the best explanation I've seen for all the "confusing" reports from owners as well as sales claims.

 

[Baker]

Baker and Codger,
Re yesterday I agree w you both. And you two aren’t the standard of normal either .. you’re both special and thank the man for different.
I did go astray yesterday and thanks for put’in up w me.

. No worries Eric. I would never claim to be "normal"....and I thank The Man every day!!!!...

 

[Aqualund1981]

120Leham Speed

I run a 42 Banks with twin 120 Lehmans and 8.5 K is the realistic top speed for those engines.
10-14 mph is about correct.

 

[Gaylord Ballard]

https://www.yachtworld.co.uk/boats/1981/grand-banks-42-classic-3662666/
Listed speed for twin 120 hp Lehmans on a 38000 lb boat, 10-13 mph.

No. The power to weight ratio doesn't compute to me.

 

[T210DRVR]

I run a 42 Banks with twin 120 Lehmans and 8.5 K is the realistic top speed for those engines.
10-14 mph is about correct.

8.5 knots is about right for that boat and a clean hull. 8.5 knots is 10 MPH. That's no where near 14 MPH. With enough horsepower I could make a rock fly, but not 120 Lehmans.

 

[BYNW]

A GB is considered a semi planning hull. With more horsepower you can get them to semi-plane along with a lot more fuel consumption. The old 1.3 times the waterline length was never a scientific formula. Sort of like the definition of a good investment is one that turns out that way.

"The informal use of the term formula in science refers to the general construct of a relationship between given quantities."

Actually it is scientific, based on wave theory. The formula: Max theoretical hull speed=1.34x√LWL calculates, for a hull in displacement mode, the speed at which the second wave starts to move past the stern of the boat.

As the boat accelerates, the bow wave increases in size. As the boat speeds up, the wave height created by the boat increases in size, so does the wave period. This will continue until the bow is supported by the bow wave, and the second wave supports the stern. Any faster and the boat's stern is no longer supported by the second wave. The boat then starts squatting and the boat tries to go uphill.

Yes, with certain design elements (IE planing or semi planing), enough horsepower to go up and over the bow wave, or under surfing condition, you can go faster.

 

[Pilon42]

8.5 knots is about right for that boat and a clean hull. 8.5 knots is 10 MPH. That's no where near 14 MPH. With enough horsepower I could make a rock fly, but not 120 Lehmans.

I have a 42 GB Woodie FL 120’s 1970 at 1800 rpm I am cruising at 10knots over water.