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Bayliner Bucaneer Cruise Speed Under Power

2K views 11 replies 6 participants last post by  chucklesR 
#1 ·
I have a 275 bayliner bucaneer with volvo penta diesel that max revs is 2500 rpm. At cruise I run 1800 rpm and get 4.7 mph under power measured by GPS. Does this seem, slow? Wondering if changing props would really be worth it. Just had bottom done and new paint put on. Max hull speed is suppose to be 7.29 mph. Would a new prop be worth it and if so how much would I pick up speed wise at cruise?
 
#4 ·
Time to 'get nautical' and set your GPS for knots! ;)

If you can't achieve rated RPM it's likely you're 'overpropped' and repitching may get you back up the the max revs. It may not give you any more speed.

Using GPS for speed can be deceiving, esp if any current is a possibility. Around here if you time things wrong you could be doing hullspeed through the water and a GPS will show close to zero.
 
#5 ·
yes.. diesels can run close to Redline for hours on end without issue. I used to drive a truck for a living and running at Redline or even slightly above for 250,000 miles certainly did not hurt the engine of the truck I drove in the slightest
 
#7 · (Edited)
You need to match your prop to the engine. if the mfg has rated your engine to run 2500 RPM's then you have the right prop. So if 2500 is correct, you can easily cruise at 2000-2100 to get more speed and not damage the engine.
Yes, you can put on a larger prop that will give you more speed at 1800, but you will be overloading your engine and only have a WOT of 22-2300. Overloading an engine is NOT a good thing. if you wanted you could put an even larger prop on that will bring your WOT down to 1800, but then you would be running at WOT.
Again, the main question is, what is the mfg's rated WOT for your engine. Until you know the answer to that question, don't do a thing.
 
#9 ·
Assuming a nice clean bottom and running gear and that your motor is running at peak, you are slightly over propped but not enough to be concerned with or to make a change. Bump up your cruise RPM another 2-300 RPM's and you will be fine with a little more speed.
 
#12 · (Edited)
Keep in mind that while diesels like to work, they like to work at no more than 90% continuously (recreational boats are fitted with either light or medium duty diesels, not the tug boat type continuous rated ones).

Your MD7A is rated at 13hp max at 2600 RPM. I'd not run it above 2340 RPM for more than 30 minutes.
If the Volvo and Bayliner engineers fit it out right you should reach your hull speed (
Your B 275 is 24.33 feet at the water line, max speed is 6.65 knots) at that RPM.

Volvo gives two different reduction ratio's - you didn't say you have the S drive (folder) so I'll go with the 1.91 ratio of the other model.

At 1800 rpm that's 942 RPM at the prop.

942 RPM * 11 inch pitch * .48 (standard slippage per Dave Gerr for a displacement boat) = 414 feet per minute - or 6.9 feet per second.
you guessed it 4.7 miles per hour

Funny how math just seems to work out isn't it.
At 2340 RPM
2106 rpm at the prop, 11 pitch = 926 feet per minute 15.4 feet per second ( 9 kts).

Since you can't go 9 knots, you are over pitched. Generally your engine came with a 14x9, just saying.
 
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