Diesel cruising RPM

[b_arrington]

I do not understand running with full tabs at cruise. I had a 2005 390 Dancer with 380 Cummins that was rated at 90% for cruise rpm. I ran that boat at 2600-2700 and the numbers were fine and I seldom used more than a small amount of tab. You can watch your GPS to find the correct amount of tab needed for the conditions you are in./QUOTE]

I think the use of tabs is boat-model specific. Some of the larger models (esp DB models) can be aft heavy and therefore run bow-high. They can benefit from tab deployment more than other models.

Case in point, my last boat needed a fair amount of tab when going getting on plane. The amount of tab when running changed depending on how many passengers. My current boat needs basically none. My father-in-law's 270 DA is pretty aft-heavy.

 

[JPGator]

I just ran a test full up/full down and the difference fuel wise is about .7 per side max. My main concern is my fuel numbers are off from charted data by about 3 mpg per side.

 

[Henry Boyd]

I think the use of tabs is boat-model specific. Some of the larger models (esp DB models) can be aft heavy and therefore run bow-high. They can benefit from tab deployment more than other models.

Case in point, my last boat needed a fair amount of tab when going getting on plane. The amount of tab when running changed depending on how many passengers. My current boat needs basically none. My father-in-law's 270 DA is pretty aft-heavy.

Brad,

Does your boat have a trim fence? The Sabre hulls are equipped with them. Basically it’s a permanent trim tab, so the adjustable tabs work less.

 

[Henry Boyd]

I just ran a test full up/full down and the difference fuel wise is about .7 per side max. My main concern is my fuel numbers are off from charted data by about 3 mpg per side.

Using the manufacturer’s or Boattest numbers will make you crazy. These tests are done under very controlled conditions when new. Our boat by virtue of being the first 38 hull with Volvo pods is the boat used in Sabre’s performance tests and I’ve yet to be able to duplicate them. But that’s with ten years of bottom paint and a seasons weed growth.

 

[b_arrington]

Brad,

Does your boat have a trim fence? The Sabre hulls are equipped with them. Basically it’s a permanent trim tab, so the adjustable tabs work less.

No, but I don’t really need one. I’ve only used the tabs on the Back Cove for a bit of leveling

 

[JPGator]

Using the manufacturer’s or Boattest numbers will make you crazy. These tests are done under very controlled conditions when new. Our boat by virtue of being the first 38 hull with Volvo pods is the boat used in Sabre’s performance tests and I’ve yet to be able to duplicate them. But that’s with ten years of bottom paint and a seasons weed growth.

I agree Henry it just bugs me that I’m 3mpg per side off. That to me is a bit off based on load and temp. Agreed that bottom paint would help for sure.