real world hull speed/cruise speed for the 4550-gctid344243

[Woodsong]

So we are mapping out our 265-275 mile trip up the TN River to get our "new" 4550 home to Chattanooga. Since we have not yet had the engines thoroughly gone over by Earl, and the boat is new to us, I don't plan on pushing the engines. Based on what I have read about the 220 hinos and the 45, it looks like the optimal hull speed works out to 8.5 to 9 knots and that will be around 1,500 RPMS, +/-, and combined fuel burn of around 4 GPH. Does that sound about right for other 45 owners with more sea time aboard the 45?

We are a bit concerned about our turbos needing to be replaced so I really don't want to get the boat up and planing until we make sure all is well. And besides, after having run our Monk 36 trawler at 6.5 to 6.75 knots for 200 hours this season, going 9 knots will feel like we are going really fast! :arr

[mmichellich]

9 knots is a bit too fast. Keep flat water/current to 8.4 or under. For even better mpg go even slower. I cruise our 47 at 8.4 knots at about 1500 RPM. Anything above 8.4 and mpg drops rapidly.

[Guest]

9 knots on the 4588 is making a pretty big wave and wake. If you want to keep the turbos out of the picture, you might want to keep speeds below 8. I recall getting very very good fuel burn on our 250 hinos on our 4588, but we had to do 6.5-7.5 knots to do it. If your time and distance will allow 7 ish knots, you will spend less on fuel, and reduce the speed on your turbos. Have a great trip.

Steve

[Guest]

I assume that since you are going upstream we are talking about speed through the water?

[mmichellich]

Speed thru the water is the only reasonable measurement to make comparisons. At least on our 310 Hinos, the turbos seem to start building boost, a bit above displacement speed RPMs. One year we had a clamp on turbo output break allowing significant leakage. Did not get smoke until almost 2000 RPM.

[Guest]

Interesting! I have seen some of these RPM's and speeds posted before.

I have 220 hinos on a 4550 and I usually travel at 7.8 to 8 knots and it takes about 1750-1800 rpms. I looked in my notes and noticed (somehow I calculated last year) that I got just over 4gph.

I just noticed that mmichellich said he has 310 hinos on a 47 so a bigger boat with bigger hinos, im not sure how that compares to mine, but:

I did notice in some earlier posts that 45 footers were saying they got 8.4 knots with only 1600 rpms??? I know my engines are running smooth, compression is great, everything checked out great, well maintained, so im really interested in hearing how many rpms other 45's are pushing to go 7.8 to 8 knots! Thats usually the speed I travel at since hull speed is 8.4

Ed

[Woodsong]

Attached is the performance chart I had seen some time ago regarding the 220 hinos which is where I was basing my original #'s off of in my first post. I guess I will see what our boat does for RPM's and speed in the real world here in the next 2 weeks or so when we start our trip! I am curious what others are turning for RPM's to get 8-9 knots on their 45's.

What is the LWL of the 45, is it not 45'? If so, the calculated theorhetical hull speed should be 8.99 knots. I need to double check the LWL for the 45. I know LOA is around 50' but LWL may be less than 45.

Attached files [img]/media/kunena/attachments/vb/646906=23821-220 Hino PERFORMANCE.jpg[/img]

[mmichellich]

A 45 does not have a 45 foot water line length. You do not include all the bow area out of the water for example, and I am not talking about the pulpit.

[smitty477]

Woodsong - welcome to the BOC again and congratulations, I am sure you will be very happy with your new Bayliner.

This topic has been recently covered in detail and a site search might also assist in your quest.

The actual mpg is very sensitive to speed over water and you will see 'breaks' in fuel use at these general speeds:

6 knots or less (7 mph) - or about 1 times the square root of water line length - best fuel use per mile travelled

6 - 8.5 knots (9.75 mph) - or about 1.34 times lwl - reasonable fuel use best at lower end

So at less then hull speeds great economies can be realized by travelling at near 1X LWL rather than at the 1.34 that is ofetn quoyed in formulaes.

As far as the charts are concerned although they are often in the ballpark I generally see something on each one of them that disturbs me is reason to disgard their intended accuracy. On the one you posted that would be the full fuel use at a too low top rpm and a too high fuel rate.

FWIW - the 45 and the 47 will have very similar fuel use and hp demand curves at the speeds which you are currently interested in.

Below is a cut and paste from an older post we made regarding speeds and gage readings. ( all will be similar except for boost)

Hope this helps

We have recorded gage readings on our 1995 4788 equipped with 310 Hp WO6D TI-II engines. The boat had a clean bottom with 2/3 fuel , full water , moderate stores. The seas were 1' or less with a 65 degree air temp, negligible tides, in salt water. The pyro gages are mounted just after the turbine wheels and the boost gages read in the intake manifold after the intercooler. Tachs were strobed last year but may be slightly off and the speeds are an average from 3 gpsÔÇÖs.

Readings with 2 engines running in gear

RPM Speed (knt) EGT Boost (psi)

800 5.4

1000 6.5

1200 7.4

1400 8.3 400

1600 9.3 550 1.5

1800 10 650 2.5

2000 11.2 750 3.5

2200 12.3 850 5

2400 15 900 8

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