Proper size for sailboat diesel ??

This morning I went to the Universal diesel engine web site and found the hp/fuel consumption curves. If your prop is sized correctly you should be burning nearly three gallons of fuel per hour at 2800 rpm. If this is not the case then you are not delivering the rated hp to the propeller or the propeller is not able to absorb the full potential horse power. The nice thing about diesel engines is that even at full speed they only consume enough fuel to maintain the set rpm, as you increase the load, the injectors increase the amount of fuel delivered to the cylinders. That is why an over loaded engine pours clouds of black smoke.

 

SSor....I have a 1969 3I7, Wayfarer built, Bruce King design....I purchased her in 2002....great boat....

 

Bobo, I bought "Bietzpadlin" in 1989 and had her delivered to my house in January 1990 I spent the next 9 years removing all of the interior wood , electrical wire, plumbing, all but one of the thru hulls, the old Atomic four, the badly scored propeller shaft, an abandoned gas tank, the existing "galley" and rebuilding her inside and outside. New water tanks , new holding tank, new head, new icebox,new force ten galley stove, new galley sink, new electrical system 12 volt DC and 120 volt AC shore power, new volvo mod.2001 diesel engine, new propeller shaft. I lined the hull completely with 1/2 inch Airex core and glassed over that with three plys of chopped strand mat and 24 oz woven roving, I replaced all of the windows with opening ports. I cut out four feet of the cockpit and decked it for a lazeret. The interior is all cypress wood. I placed all of the chain plates on the outside of the hull and replaced all of the standing and running rigging. Other than that it is all original!
Ross Hill in
Bel Air, MD
nan@ross@starpower.net

 

The engine is a good match,but you should motor at 6-6.5kts at 2500 rpm's. do you know what the reduction gear ratio is? Do you know the Diameter of your Prop? If the bottom is clean, the engine is in good condition, and the boat is not excessivly loaded with stuff, then the problem is likely that the reduction ratio, prop. diameter and pitch are not mated very well.

 

Name: TORTOISE

--------------------------------------------------------------------------------
Home Port: Portland, Oregon

--------------------------------------------------------------------------------
Owners: Dave & Sue Larson
Address: 8770 SW 133rd, Portland, OR 97008-7529, USA
Phone: 1-503-644-9364
Email: dlarson@grpmack.com


Hull: type when purchased when launched hull builder material
hard chine n.a. 2001 owner wood

--------------------------------------------------------------------------------
LOA LWL beam draft capacity speed weight
38.5 feet 34 feet 11.5 feet 2.5 feet 6 adults 8+ knots 15,000 lbs.

--------------------------------------------------------------------------------
Other: The hull framing is constructed of recycled fir timbers: 2"x6" frames, 3"x6" keel. The skin is 15mm okume 1088 plywood. All materials secured with bronze fasteners and West System epoxy. Entire hull is covered with fiberglass.

Engine: type year built builder # of cylinders bore & stroke valve type(s)
compound 2000 Pat Marooney two 3" + 5" x 4" "D" slide

--------------------------------------------------------------------------------
ihp rpm reverse type condenser type & size vacuum
10 500 Stephenson inboard shell, approx 10 sq.ft. ?

--------------------------------------------------------------------------------
Other: Two Tiny Power Model 3454 engines, each driving a propeller direct coupled. Air pumps are Navy (Bailey) type from the John York casting sets.


Propulsion: dia. & pitch # of blades material make RH or LH shaft size
20" x 26" three bronze unknown RH & LH 1.375"dia
--------------------------------------------------------------------------------
steering auxilliaries paddlewheel (dia., width, & # of buckets)
cable steam driven alternator to provide both d.c. and a.c. power.

Boiler: type builder year built bhp operating pressure gauges
Series D650 Bryan Steam 2000 15 175 psi five
--------------------------------------------------------------------------------
overall size # & size of tubes Heat.Surface economizer HS superheater HS
40" x 35" x 52" n.a. 58 sq.ft. none none
--------------------------------------------------------------------------------
fuel grate area stack dia. & height pump type injector type tanks
oil n.a. 8" dia. x 7' Pumptec Model 112 none 100 gal.

Additional: Launched October 26, 2001.


This is a fine example of the results of properly matching propeller to boats and shaft speed. ten hp steam @ 500 shaft RPM, 7 1/2 tons 8 kts. lwl 34 feet.

 

32hp is more than plenty. Even a 20 hp would be fine, unless you actually NEED to go over 6 kts.

 

Doug, Somehow I missed your post, You are quite right we have a good match. The reduction gear is 3:1 the propeller is 13x15, the wl is 26ft. I think that 13x14 would be a better match but for 75 bucks I won't change. We get hull speed at 2500 engine and just bury the stern above that. It is a good combination for getting off the bottom here in the Chesapeake. What you don't go aground? then you don't cruise the Chesapeake!

 

How about 1-1/2 vs 3 gallons/hr at 2500 rpm?

Wow! We're no where near 3 gph at 2500 rpm. I'm having our mechanic check the 5432's compression, vs the "design" compression of 448 psi. If that's within say 10%, then we'll increase the MaxProp angle from 12o. Any other ideas?

Captain Rich

 

The answer then is you are not using anywhere near 30 hp. I think that your engine is fine but your prop is too small. Increasing the diameter has a much greater effect on thrust than increasing pitch. Example 12" prop vs 13" You square both diameters and you get 144 vs. 169 . 144X12 pitch =1728
169X12=2028 Then 144X13=1872 . If you can fit a larger diameter prop or if you can increase blade area you can absorb more hp. Most diesel engines consume about 280 grams of fuel per hp per hour.

 

Beware of putting too big of a diesel engine in your boat. We did it once, and after about 200 hours it wouldn't start from lack of compression.( piston rings never seated, ring-grooves caked up with **** and the rings broke in several places)

Yokebutt.

 

Root Cause ??

Ssor,

We replaced our original Michigan? two-bladed, 18" dia x 12" pitch, fixed prop with a three-bladed, 17" dia x 12o pitch, feathering MaxProp. It significantly reduced the strong, prop-induced hull vibrations (which quickly fatigued you), but it might not be a close enough match.

The engine maxes out at 3,000 RPM, no load, and at 2800 RPM with the 12o pitch setting. Earlier we had a 14o pitch where the engine only maxed out at 2500 RPM.

Is there anyway to correlate the two props performance?

Captain Rich

 

Rich,
Do you know what you reduction gear ratio is? Theoretical speed through the water, no slip, is 1 knot per inch of pitch per 1000 rpm. Your boat is really not much larger than Bietzpadlin (30 ft. OD 4 1/2 tons) , I figure that you propeller should absorb about fifty per cent more power that mine does. At wide open throttle you should be digging a hole in the water. When you maxed out at 2500 rpm were you making a lot of black smoke? If you are running without a reduction gear you may be suffering from excessive slip. 2500rpm x 14" pitch=35 knots theoretical speed. That's a lot of enegry being used to stir the water but not to push the boat.
Ross in Bel Air

 

Capt'n Rich,
We sail out of Perryville, Md. Do you sail the chesapeake bay?
Ross in Bel Air

 

Capt'n Rich, I had another thought about your boat speed. I know that you are dissatisfied with your boat speed at wide open throttle, but have you made note of your speed at in-gear but idling, at 1200 rpm, 1500 rpm, 1800 rpm, etc. If the speeds are then plotted, rpm vs speed, you should get a nearly straight line curve and speed at 2100 rpm, and 2400 rpm should be predictable. If the curve flattens out then you are probably starting to slip the propeller.

 

I don't know too many 37' sailboats that cruise at over 7kt!

I know a former O'Day 37 owner, who used his boat a lot, including a lot of rallies and racing. I'll ask him how his went under power.