Advice Cummins 6BT low speed boat

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Basshunter1

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Hello,

I bought a boat last week with a Cummins inboard 5,9 liter 6BT. The boat is 32 foot long and approx. 10 foot wide. De clutch is a velvet with a Unnown delay. The boat runs max 7 knots at 2600 rpm and 9 knots at 2900/3100 rpm. I do not know displacement but it must be arround 8/10 ton. I want the boat to go faster 20/22 knots for longer fishing trips. How do I upgrade the speed of the boat? Hope anybody can give me advice on that. Thank you. Kind regards Hans
 

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A little bit my old boat was a planning boat but mutch smaller a 5,40 alpha fish a Beekman ( dutch Brant) I think this boat is a half glider. The prop is for trolling 5 blades. It used to be a srimp boat with trolling net.
 
ok Txs. 600hp that’s a lot. There is a trim area in the back but It is a fixed Trim. I don,t think this boat can handle 600hp
 
What makes you say 8/10 tons, I would have thought 5 maximum which changes things dramatically. Maybe only 350hp needed. You may get better performance with the current engine/box if you fit adjustable tabs to give more aft lift and possibly a different propeller. Does the engine reach maximum revs and no more. If so that is correct. If it over-revs or under revs then the prop' is wrong. Plenty to think about!
 
The 8/10 ton is just a wild gues, by the size of the boat. I realy don,t know the official number. Nobody can tell me the Brant of the boat, a lot say Englisch but I can,t find it. Yea I was thinking about changing the trim system and prop. I can also measure the current delay of the velvet drive and change delay to 1:1, in combination prop trim I hope a bit more speed.
 
Given your figures in the first post you are over reving it so given it's history this could be prop or gearbox ratio's. Knowing what boat it is (and then displacement. semi-displacement hull) would help because a large displacement / hp engine may have been there precisely because it needed to drag nets rather than power to get on the plane.
 
BruceK said:
Given your figures in the first post you are over reving it so given it's history this could be prop or gearbox ratio's. Knowing what boat it is (and then displacement. semi-displacement hull) would help because a large displacement / hp engine may have been there precisely because it needed to drag nets rather than power to get on the plane.
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Ok thank you, yes the boat was used to troll nets for scrimps. So that’s why the velvet is delayed and the 5 leave prop. Thank you for the advice. What we are going to do this week is measuring the rpm of Fly wheel rotation and Axel to find out the delay of the velvet. After that lift the boat to see the prop And look for another prop. I do know that the last owner replaced the velvet because old one broke down. He said with the old velvet the boat ran 13/14 knots already better. I have the old velvet at home but there is no plate on it where I can see the delay. Only the pour numbers from casting iron.
 
My 32' has two 6BT5.9s and just about gets to 18 knots.

With only one it would not get on the plane, so I expect you are stuck with the speed reported.
 
Fwiw I have 2x 330hp in a 40ish ft 13ft beam deep vee (18deg) flybridge weighing around 12t flat out at proper wot is about 27kts and I generally cruise at 2200 to 2400rpm which gives 16-18kts props are 21x20 4 blade, gearbox is zf220a but no idea on ratio.

Mine is a planing Hull though. The 3706bta is already fairly highly strung so I wouldn't be trying to get more power. Make sure aftercooler is properly clean and serviced and make sure you can hit above WOT as per Cummins spec (I think it's 3100rpm) boat needs to be loaded and at needs to see 50 to 100 rpm above that. If you can't make the proper WOT then you are already overpropped for the weight / hull. You will have to live with what you have.

Try a post to tony on sbmar but you will need lots of pictures and lots of accurate information. He does many repowers so knows his stuff, but can be short in his answers should he not get accurate info or correct answers to his questions

Steve
 
5teve said:
Fwiw I have 2x 330hp in a 40ish ft 13ft beam deep vee (18deg) flybridge weighing around 12t flat out at proper wot is about 27kts and I generally cruise at 2200 to 2400rpm which gives 16-18kts props are 21x20 4 blade, gearbox is zf220a but no idea on ratio.

Mine is a planing Hull though. The 3706bta is already fairly highly strung so I wouldn't be trying to get more power. Make sure aftercooler is properly clean and serviced and make sure you can hit above WOT as per Cummins spec (I think it's 3100rpm) boat needs to be loaded and at needs to see 50 to 100 rpm above that. If you can't make the proper WOT then you are already overpropped for the weight / hull. You will have to live with what you have.

Try a post to tony on sbmar but you will need lots of pictures and lots of accurate information. He does many repowers so knows his stuff, but can be short in his answers should he not get accurate info or correct answers to his questions

Steve
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Thank you for your advice Steve, yes good idea to measure displacement correctly and accurat to get more information about it. When the boat is out I will measure hull and make a lot of pictures. And pm them. Also my investigation about Brant of the boat continues. Going to check the after cooler to thanks, it cooles now, but do not know if it cooles normally. The temperature With 4/5 hour runs is arround 87/89 degrees
 
PCUK said:
Just to confirm the after cooler cools the intake air to the engine. Yours may not have one. The heat exchanger cools the engine and you definitely have one of those.
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Sorry not sure why I thought it was a 370hp engine..

Only the 210 came with no aftercooler, the 270 had a JWAC type and 300up had the seawater cooled.

Steve
 
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