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Old 01-26-2015, 09:04 PM   #1
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Slow boat

Hello all, I just completed a great holiday from Lake Macquarie to port Stevens ( ocean coastal) -myall lakes and back home. I love the boat - a Chung hwa clipper 30 with the 80hp lehman but the time to get up there 9hrs is a bit tedious for a 45 nm journey. From a more experienced point of view is there any avenue worth pursuing to get a bit more speed? I expect the only way is to change props and or engine or new boat. I know it's probaby a dumb question otherwise we'd all just have 80hp engines pushing big cruisers along at planing speeds by changing props- but another 2-3 kts would be good.
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Old 01-26-2015, 09:20 PM   #2
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Cheapest solution is most like to be buying a boat capable of higher speeds.
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Old 01-26-2015, 09:26 PM   #3
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Welcome aboard Bluevee. Nice boat, what was you're average speed and fuel burn? Going slow allows one to smell the roses. When we sailed at about a 6-7 knot pace it was nice until "all hell broke loose".
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Old 01-26-2015, 11:01 PM   #4
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My average from the navionics app says 5.9 kts over 41.1nm. fuel burn is about 6 litres / hr - (about 1 1/2 gal) which is probably an enviable amount from most boat owners. I run the engine at 1800 rpm and the bottom is clean. It's a great boat but I would love to take her further afield in a bit less time.
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Old 01-27-2015, 12:20 AM   #5
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Today's run from Vallejo to Benicia/Martinez and return (exercising engine and observing/enjoying nature's and man's doings in Carqinez Strait) averaged 4-plus knots SOG against the current and eight-plus knots with, at about 1.5 gph for 6.3 knots through the water. Weather was cool, but having the pilothouse doors closed kept us comfortable. Pitied the one sailor seen in an open cockpit. ... When buddy-boating with friends, I generally leave earlier so their faster boats can catch up.
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Old 01-27-2015, 12:34 AM   #6
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Greetings Bluevee-
As a fellow boater in the process of changing out a Perkins 4-154 (58hp) to a Perkins 4-236 (85hp) in a 27 foot Marben, your challenge sounds familiar in that with the 4-154 we are making 5.9-6.5 at 2150 RPM and have to turn 2400 RPM to make 6.9 (Hull speed)
Part of the process in making the decision was to confirm that the change would utilize the current wheel.
We use this site for the formula to determine which wheel will work. The outcome of the formula is very actuate in my opinion. Give it a try to see where you are with your current wheel.

Vicprop - Propeller Calculator

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Old 01-27-2015, 12:39 AM   #7
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I just found these specs for a Ford Lehman 2712E which indicates it is rated at 80hp @ 2,500rpm. It can produce 60-65hp @ 1,800rpm with SFC of .41lb/hp/hr or 3.79gph and 16.5hp/gal/hr.

If you were really only burning 1.5gph at 1,800rpm, assuming 16.5hp/gal/hr, the engine was only producing 24.75hp. That sounds about right for that size boat at 5.9kts.

I was able to find a couple of Clipper 30 Sundeckers listed in Oz which advertise a 7kts cruise and 9kts max with a 38hp Perkins diesel. Not sure how comparable these are to your model.

Can your engine turn the rated 2,500rpm at WOT? If not, you need to find out why not. It could be the engine, the prop or both.

Even the relatively heavy 30' Willard/Fales boats will easily make 7kts with less than 40hp.

You also might run your boat's specifications and measurements through the calculator at Victoria Propeller and compare it with what you have now. It should at least provide a starting point.

Keep us posted on your findings.
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Old 01-27-2015, 12:53 AM   #8
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Perhaps I can offer my contrarian view here. My boat was originally equipped with a 260 horsepower GM 350 capable of taking my boat well over 20 knots. I never enjoyed travelling faster than 6 knots. Taking in the beauty of the surroundings, having a good time with guests as I'm at the helm are a big part of the fun on a cruise.

I decided to be true to my desires. I love my boat and had put a tremendous amount of time and effort toward restoring it. So, I felt a repower was in order. I had the 260 horsepower engine replaced with a 48 horsepower Perkins 4.108 Diesel. Now, I burn less than a gallon per hour, cruise at about 5 knots comfortably, and enjoy every moment of it. I plan my excursions with tides in mind, so I'm not stuck against a heavy current.

I enjoy the boat more and have no desire to ever go back to cruising at high speeds.

Enjoy your slow boat and get as much as you can out of it. I agree with Mark. The most cost effective way to increase speed is to replace the boat.
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Old 01-27-2015, 01:10 AM   #9
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Going slow gives wildlife time to get out of the way. Sea Lion under attack by seagulls:


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Old 01-27-2015, 01:29 AM   #10
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Astrial Blue- You are making my point on another subject submitted many months ago regarding the thought of purchasing one of the large 38-40 foot wood cruisers such as Chris Craft in boathouse condition having twin 454 gas hogs. Due to the price of fuel (Changing?) these boats were often on the market begging for a buyer. The thought of buying one on the cheap, then picking up two Perkins in the four cyl model (4-108/4-236) or the Japanese/Caterpillar models of the 4-154 and converting as a project to these smaller engines achieving about the 5 knot speed but acquire the full Monty of creature comforts these big sweet old classics hold. Just a thought that was pretty much shot down which is okay the conversation was enjoyable.

On your conversion you acquire the desired goal. In our conversation efforts we wish to obtain the hull speed at a reduced RPM. Changing out the 4-154 (58hp @3000RPM) for the 4-236 (85hp@2500RPM) will allow us to utilize a 2:1 gear over the current 3:1 gear. As we are turning the same shaft and wheel, we will obtain the same hull result we current have so we know that is a fixed result. However, as I indicated we turn the current shaft 2400 RPM to achieve hull speed (6.5-7.3 depending on tide) where as with the 85 hp 4-236 we will obtain this at 1600RPM. At 2400 RPM with the 4-154 we are close to 2 gallons fuel burn. At 1600 RPM with the 4-236 we anticipate no more than that and perhaps less. It would seem we will continue to cruise at hull speed at a lower cabin sound, with less fuel burn.
At any rate I too leave the harbor before the faster boats and allow them to catch up.

LarryM seems to have a bit of knowledge on fuel burn and I’d like his take on the above assumption. This is said listening to 4-236 owners claiming 1 gallon fuel burn at between 16/1800 RPM. I am skeptical on owners claims on fuel based on my personal fuel burning records at various RPM settings. Just seems everybody likes to shave a tad off the actual MHO.

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Old 01-27-2015, 01:34 AM   #11
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Sorry Didn't mention that the Perkins 4-154 is a model of 1960-66 or the second level that ended in 74 (Hard to tell Perkins early SN information. The replacement engine is a checked out okay 2003 with very low hours.
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Old 01-28-2015, 09:48 AM   #12
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Thanks for the replies and info- I've been looking at prop options here according to the vic props calculator, it seems to indicate a possible 9.5kts at 2100 rpm with a larger courser prop- we'll see. I don't want hit the wildlife- especially the 5+ meter white pointer that has been keeping us off the beach here at Newcastle chewing up dolphins
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Old 01-28-2015, 10:46 AM   #13
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Bluevee,
Your boat is wide, short and perhaps heavy. Not built for speed (like mine). Find one that is narrow, long and light.

Our boat cruises at 6.15 knots and most all the time I'm very happy w that.

But the easiest way to solve your problem is to just shorten your destinations. Or/and cut them up into shorter segments. But available daylight an the distances between harbors or/and anchorages often have a say in that. Just be flexible.
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Old 01-28-2015, 10:49 AM   #14
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We normally do about 7.3, but once we start doing long range stuff we'll probably do ~6.5kts or so.
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