Choosing the correct Gears?

[John Nardi]

Hey Guys...In the process of shopping for engines...If I go ahead and get either Cummins 6BTs in the 270-330 range or Cat 3116 at 300-350 HP what are the considerations I should be evaluating in deciding on choosing a 1.5 or 2/1 gear ratio. I will be slow trolling from time to time for grouper in the Bahamas so I want to make sure I am making the correct choice with or w/out trolling valves...Thanks in advance...John

[Bob H.]

John, I went with zf 220a. down angle 1.5:1 gear ratio, I did go with trolling valves. Make sure you put a BIG red light on dash so you or anyone else running boat won't smoke the gears when trolling valve is on. Hope this helps. BH

[John Nardi]

Thanks Bob

[Tony Meola]

John

I have the same as Bob in my 31, with the 270 Cummins. I don't have trolling valves and on one engine I am at about 3.5 knots. Both engines close to 5 knots.

[Bertramp]

Hi There ....
Tony, with your Cummins 270s, what is your cruise RPM, what is prop size and what is your cruise speed ?
thanks

[Tony Meola]

Steve

I am running 20 x 23 with a slight cup. They top out at 2650, they are rated for 2600. The Cummins dealer told me I could run them at 2400 all day long without hurting them. I usually cruise around 2200 to 2300.

As I have posted in the past, I am running light no tower or hardtop, just a soft Bimini. The RPMs basically almost tie to the knots. At 2100 I am at 21 knots at 2200 22 knots at 2300 I am a little over 23 knots and at 2400 depending on the tide I can be anywhere from 24.5 knots to 26 knots. She tops out at just shy of 30 knots.

[Bertramp]

Thanks

[John Nardi]

Thanks Tony

[Tony Meola]

UV had the 250 Cummins and used to say the weight did not matter he always made the same speed. I find that as she lightens up she runs faster which makes sense. When she gets down to a half tank I find making 25 knots a piece of cake.