Prop pitch, GPH, cruising speed, RPM

[dodgetkboy78]

I have recently bought a 1970 hardtop express. It is registered as a
28', 9'8" beam boat, from what I can tell, it is a 27'3" boat.

But thats not the question.

It came with a 225hp 318, and recently has had an update to a 360. The
transmission, prop, ect, was all left alone.

Top speed, if you got the guts to rev it that high, is around 24kts,
at 5100rpm. Yeah, ouch.
To stay on step, it takes 3300rpm, at about 13kts.
I have been cruising at 7-8kts, at 1800-2000rpm. Throttle is barley
open, and it burns around 4GPH at this speed.

Here is my question.

Does that sound right? It takes the 4bbls open a bit to keep it at
13kts. I just cant bring myself to run it that hard, for long periods
of time.
Could I pitch the prop to make it cruise better at 12-13kts? Or would
it just take more throttle at less RPM?

Either way, the 360 almost seems to big/too little.

I can be happy with it at 7-8kts, but was wondering if it was, well,
normal.

Other than that, this is the nicest handling, roomy, well built,
smooth riding boat I coould ever imagine, takes 4' following chop like
a champ, turns on a dime, and has a real "Heavy" safe feeling in the
water. My plans are to put a 330hp cummins in it eventually, that
should push it 15kts, and burn the same as the 360 at 8 I bet, but for
right now, I want to get the most out of my 360.

[Marc Rovner]

I get 24 mph on gps running at 3400 - 3500 rpm with my 318. thats with
3 or 4 people and lots of stuff. prop is 16x15 not cupped. something
is wrong with your numbers. i will be playing with my timing and plus
tomorrow and hope to get a steady 25mph at 3600, with engine purring

[e b]

hi,

 

I have a 27 express cruiser, not sure if your boat is the same, I removed the twin gas engines and installed a cummins / dodge 6bt in it, did the marine conversion myself and tweeked the pump a bit so I might be in the 250 to 300 hp range. it will do 20 knots, I cruise between 8 and 9 knots at 1400 rpm and about 2.5gph, headed down to the sea of cortez this afternoon for 10 days island hopping trip...im sure that if I cruised 7 knots I would easily get 2gph..

regarding your present set up and speed, anytime you ask the boat to go over its designed hull speed, in our case about 7 knots, your fuel requirements go up drastically, nothing you can do about it...!

it sounds like you are propped right as it is if you can just reach red line at wide open throttle, the only "sure" way to increase efficiency is to spin a larger, slower turning prop, but that means different gear ratio, you would gain hull speed fuel efficiency but loose some high speed efficiency...

im running a 19X21 prop right now.

Eric----- Original Message -----

[e b]

single or twin engine...?

[john hamilton]

I tried replying once but my long message disappeared into cyberspace.  I'll try again with a  shorter message.   I have a 1970 27 Express Cruiser.  27' 9" long, 9' 3" wide.  Single reverse rotation 360, Borg Warner 71C, 1.5 to 1 ratio, 16x14 RH prop.  Minimum planing speed was 13 knots, cruising speed was 15 knots at 3400 rpm, top speed 23-24 knots at 4300-4400 rpm.   I saw an advertisment for a 1969 27 Express Cruiser with a new 350 hp 454 Chevy based Mercruiser inboard.  Claimed performance was 18 knots cruising speed, 25 knots top speed.  I think your performance is about right with that 360.  I've made trips up to 110 nm at 3400 rpm (5-7 hours straight), with no problems.  It's not the running that kills them, it's the sitting!   I rebuilt my engine in my garage with more compression, longer stroke crank, custom camshaft, other goodies.  Standard rotation engine now, lightened 250 pounds and set back about four inches, ZF63A transmission, 1.5 to 1 ratio, 16x16 RH prop.  Minimum planing speed same 13 knots, cruising speed up to 19 knots at the same 3400 rpm, top speed up to 30 knots at 5000 rpm.  With bigger custom gas tanks I now have 60% more range with my cost per mile down 50 cents despite higher priced 91 octane gas.   Your setup might be around one or two inches too shallow on the prop.  Stock Chrysler marine camshafts have a power band that tops out in the 4400-4800 rpm range.  The more powerful 360 needs more prop than the 318.  I would try cupping the existing prop.  If you're still topping out above 5000, try pitching it an inch at a time till the top end is down to 4800 or less, then running the 360 till it dies.  It might outlast you! John --- On Thu, 9/10/09, dodgetkboy78 <valleyresid...@yahoo.com> wrote:

[dodgetkboy78]

Sorry, it is a single 360.

Also, since it sounds like there is a ton of chrysler marine
experience here........... (I am a chrysler guru, but this is the
first marine engine I have ever messed with)

This 360 has heavy cast iron rockers, is that a marine thing? (Ticks
like a mech cam too, I haven't opened up a cover to see if it does
have one, or has lifter/adjustment issues)
It also has a single plane intake, I think it came off of the 318,
(Which has different port size in the auto world). The manifold looks
like the 2bbl single plane on the 215hp 318's, and just like the 273
manifold. It is on the 360 now.

Is 7-8kts a good speed? I am happy with it, I just was wondering if it
was supposed to be a slow boat, or it was because it is under power.
Last boat was a 1976 Bayliner 22', with one of those little inline
volvo AQ170hp engines, it ran like stink, 14-16kts, and it took more
power to run at 7kts. But it was too small, took rough water like
crap, and was a Bayliner. I go out in the Prince William Sound, so
choppy water is normal, and it is nothing for 6'-8'ers to come up in
the middle of the trip.

What is "Cupping"? I am new to boats this small, also, another inch on
the pitch I too think would make a difference.

The main issue I have with running it 3300, is the 4bbls are kicked
in, and it seems to be burning about 12gph. I am getting about 1/2
gallon per mile at 7kts.

As far as the cummins, my truck has a 350-375HP tweaked VE pump
cummins, I just wonder how the bellhousing/transmission thing will
work. I guess find a twin disc from a yacht re-power? Being a trailer
boat, I cant run a huge prop.


Picture: http://s12.photobucket.com/albums/a227/dodgetkboy78/?action=view&current=l_28b39ea8f8be461bb97a15af905e6228.jpg

[e b]

Hi,

 

I was asking Mark if his boat had single or twin engines since his numbers differed so much from yours and seemed unrealistic for a single engine boat...

"cupping " a prop is giving a little flare to the edge of the prop and acts like having extra pitch, as far as speed, a boats efficiency is best at or bellow hull speed, since you had a small boat you could feel that bellow lets say 5 knots, the boat moved very easily, but to get up on plane you had to gas it, the boats stern would go down and kind of dig in untill you gave it enough power to climb on top of the water and break free... basically what is happening is that as you go faster, the water does not have time to fill the hole the boat has created, so the boat kind of sinks in the hole unless you have enough power to break free and plane above the water.

the theory is 1.37 X square root of the water line length = your hull speed.

most power boats are planning or semi planning hulls, most sailboats are displacement hulls, you can put 1000 hp in a 30 ft sailboat and all it will do is create a big hole it keeps on trying to get out of...

if your water line length is 24ft, your hull speed is 6.7 knots...

to adapt to marine use, you will need a SAE bell housing, I believe cummins uses a #2 on their engines, fairly readily availlable at semi wrecking yards, the bell housing off a 4bt works as well, a lot of industrial equipment like gradals, skytrax and extended reach fork lifts use 4bt's.

I do believe someone make an adapter to use the dodge bell housing...

Eric

[Oliver]

Hi,

I got a 31' with twin's. For me 7 -7.5 knots works perfectly as it
runs in total displacement. The hull speed is mainly defined due to
the length of the waterline of the boat.
Your 27' has probably a 25' waterline, my guess is that 7 knots is
slightly over your hull speed for displacement you should get a better
fuel mileage @ 5.5 - 6 knots at around 1500 to 1700 rpm's.
These boats are not displacement boats but this way you get he best
fuel mileage.

12 gph on plane sound ok, 3300 rpm's are just fine, I run @ 3600 rpm's
if i'm in a hurry and yeah they are purring and suck somewhere between
16 - 18 gph, it's a big boat and there is not really a trick
to get it on plane without open up the 4 bbl's.

5000 rpm wide open sound's high but my 318's get up there in a hurry
as well. I' don't think that you are getting a better fuel consumption
with a different pitch. The engine has to work harder and you lose
your vacuum,
meaning the air gas mixture is to rich, more gas is going through the
exhaust unburned. I had a 24' CC Fiberform with a 350 last year, max
rpm 4200 rpm and it sucked 12 gph easily as well.

Anyhow if you decide to do something about your props I agree with
John, get them cuped that should get you down to 4800 max rpm but
remember your only supposed to run wide open for a short period of
time ( 15 min.)
Every thing between 3200 - 3800 rpm is fine to run for hours, actually
that is the range these boat's are meant to run, they love it and if
your fuel budget is happy with it go for it.

Re power with a big diesel, well if you buy everything new and use
your boat for 100 hour's a year the point of return for the investment
is most likely between 150 to 200 years. I thought about doing the
same but no way that
I burn that much money and after wards have to listen to a noisy
engine and will never really save a buck. I like the sound of the
318's and since I'm not in a hurry most of the time the 3.5 -4 gph @
7.5 knots won't kill me.

Have fun out there

Oliver

[dodgetkboy78]

I put a lot of hours on it, in fact, last weekend I put 27.5 hours on
it, ran like a top other than a relay. The reason I want to go diesel,
is safer, no ignition system to go out, and no need to carry extra
fuel. It holds 110 gallons.

I found a 2700 hr 555 cu in cummins, with an extra with a broken
crank, both twin discs, for 2K. A Big yacht take out. Problem is, the
transmission, seems most are like 2-1. I really would need a 1-1, to
use the small prop, not to mention peak torque would be around
2000rpm.

I don't know, I was mostly wondering if it was normal to cruise these
things at displacement speed, or to run the crap out of them.
1MPG or 2MPG.............. LOL

[dodgetkboy78]

"I rebuilt my engine in my garage with more compression, longer stroke
crank, custom camshaft, other goodies. Standard rotation engine now,
lightened 250 pounds and set back about four inches, ZF63A
transmission, 1.5 to 1 ratio, 16x16 RH prop. Minimum planing speed
same 13 knots, cruising speed up to 19 knots at the same 3400 rpm, top
speed up to 30 knots at 5000 rpm. With bigger custom gas tanks I now
have 60% more range with my cost per mile down 50 cents despite higher
priced 91 octane gas."

What stroke crank did you use? I have a 318 in my truck stroked to a
390, 4"x3.34. The issues I have had with it just being a work truck
motor, I am not sure I could trust it in a boat. Well, crap pistons
from KB had something to do with it. Just curious what was in your
360.

From the sounds of it, I should find and build me a 273, and just plan
on running it in displacement.

[bmwbio...@gmail.com]

Wow!
You little guys got the @hit!
55K lbs and 900 horse gets me 12 cruise and 24 top.
Don't want to talk fuel consumption. Love to read about your handy work on the trannys and engines.
Very happy cruising fellow unies!!
Kevin
Sent from my BlackBerry® wireless device

-----Original Message-----
From: dodgetkboy78 <valleyresid...@yahoo.com>

Date: Fri, 11 Sep 2009 18:06:22
To: UnifliteWorld<unifli...@googlegroups.com>
Subject: [UnifliteWorld] Re: Prop pitch, GPH, cruising speed, RPM

[john hamilton]

Eagle four inch cast steel crank, Eagle rods, 4.04 bore with KB quench dome pistons equals 410 cubic inches in a 360 block.  The compression ratio is 10.5 to 1.  Since my cruising rpm range isn't that high at 3000-3600, there's really not that much stress on it so I didn't need to get expensive forged pistons or a forged crank.  The cam was custom ground by Dave Hughes www.hughesengines.com for peak torque at 2500 rpm.  I did that because that's when the maxium load is when the boat's trying to climb up on step.  According to my desk top dyno program I have 505 lb-feet of torque at 2500 and more than 450 lb-ft from 2000 to 5000..  I didn't build a hot rod so much as a tractor motor with a wide power band.  The high compression ratio was for fuel efficiency more than horsepower.  The cooling systems on these Chrysler marine engines are pretty good, and with me running in water that is pretty consistently cold year round I wasn't that worried about detonation issues.  I run a 180 degree thermostat (stock for a fresh water cooled engine is 160, raw water cooled engines were 140) and my temperature stays about 130 degrees no matter how long I run it.  I got some aluminum gas tanks made to fill the available space and my bunker is now 136 instead of 100 gallons.   In my humble opinion, the 27 is at it's best cruising 15-18 knots in a two or three foot chop.  The boat is heavy for its size and has a fairly sharp entry so it's really comfortable in choppy water.  You will run right by the aluminum runabouts and lightweight Bayliners that can't take the pounding.  Chrysler made a great marine engine and it will live a long time running 3000-3800 rpm.  Run the crap out of it! John

--- On Fri, 9/11/09, dodgetkboy78 <valleyresid...@yahoo.com> wrote:

From: dodgetkboy78 <valleyresid...@yahoo.com> Subject: [UnifliteWorld] Re: Prop pitch, GPH, cruising speed, RPM

[john hamilton]

Run the crap out of them!   I used to run patrol boats on Lake Washington.  We had 350 Chevy based Volvo sterndrives (YUK).  We cruised at 3600 rpm and got 3000 plus hours between re-powers.  Top end was 4500 rpm and we ran half the length of the Lake at WOT routinely.  Seattle PD ran 34 foot Uniflites with twin 440 Chrysler inboards for years in the 70's, 80's and into the 90's.  Those engines ran for thousands of hours and they also cruised over 3000 rpm.  They spent a great deal of time putting around at 1500 rpm as well, but the point is the marine engines are designed to run much higher for much longer than the pickup truck engines.  Run the crap out of it!  When it dies, rebuild it!  Unless you're made of money and want to pay more than the boat is worth to put a diesel in it.  Nothing wrong with that, but it's well beyond the capacity of MY cash flow.  Good luck!

John --- On Fri, 9/11/09, dodgetkboy78 <valleyresid...@yahoo.com> wrote:

From: dodgetkboy78 <valleyresid...@yahoo.com> Subject: [UnifliteWorld] Re: Prop pitch, GPH, cruising speed, RPM To: "UnifliteWorld" <unifli...@googlegroups.com>

[dodgetkboy78]

Anyone ever tried kort nozzles? Since it is a slow boat mostly, I was
thinking of playing with one.

[bmwbio...@gmail.com]

????
Kort?
Slow boat?

Sent from my BlackBerry® wireless device

-----Original Message-----
From: dodgetkboy78 <valleyresid...@yahoo.com>

Date: Sun, 13 Sep 2009 20:29:46
To: UnifliteWorld<unifli...@googlegroups.com>

Subject: [UnifliteWorld] Re: Prop pitch, GPH, cruising speed, RPM

[sear...@buckeye-express.com]

Hi dodgetboy; Welcome to the world of Uniflites. I also have a 27 uni 1972 with a pair of 318's, direct drive {1:1}

velvet drives, 1-1/4" shafts turning 14" x 10" cupped 3 blades. It originally came with 14"x11" props. It will plane at 13 mph @ 2200 rpm, but not an efficient speed to run. Normal cruising speed is 18-20 mph @ 2600-2700 rpm. WOT is 32 mph @ 4000 rpm. Measured with sumlog and GPS and digital tacks. The boat has the long cabin. hard top with bridge and duel controls.
These hulls are 27'-3" long with a 9'-7" beam. They are very strongly built yet quite flexible and with a hard gel coat {which will shine up well } they tend to get many flex cracks. Your single 360 sounds great. I would think you have a reduction gear of 1.5:1 or more. As I understand, you should turn as big a diameter prop as you can in the space, but allow 15% {per Michigan Wheel }
of the diameter for clearance from blade tip to hull. Then adjust the pitch for a WOT of 4000 rpm. I would really load that engine up, because the 360 has almost twice the low end torque as a 318. Take the prop to a good Prop-Shop and tell them of your 5100 WOT, your gear ratio and what WOT you want, and they should be able to re pitch it. Good luck! Ray














]

--- valleyresid...@yahoo.com wrote:

From: dodgetkboy78 <valleyresid...@yahoo.com>

[Marc Rovner]

Hi, my response took a while as I had to do surgery on my macbook. I have a single 318. I am not sure where exactly the difference in performance comes from. When i bought the boat I figured I made the biggest mistake ever. Max 10 knots, engine sounded like it wanted to detonate, wiring was haywire etc. Currently she purrs at anything up to 3800rpm (never gone full throttle) and really does get the numbers I posted (mph not knots had gps set wrong and left it that way). 

Can anyone please give me an idea as to total timing at what rpm, I finally realized that the middle of the range spring on the aftermarket distributors is way too stiff. I figure all in should be around 2200 - 2400rpm so you need the lightest spring possible. Any  one have a thought on plugs - ngk vs' whatever and what plug number. I must admit having spent some time cursing and then tweaking the 318 I now think it is exceptional. It just purrs at the 550rpm idle and will even go down to 450 and be so smooth (yes, still has good oil pressure). Any tuning/performance thoughts greatly appreciated.

[dodgetkboy78]

I would set total at 34*, peak performance would be 36*, but 34*
leaves you room for error, and fuel quality. Depending on your
throttle setting, your timing should be all the way in by 2300 or so.
If it takes 1/2 throttle to get 2300, you may have to back it off
some.
The timing on this 360 is full advance by 2000, and it runs 2K with
the throttle barely open in gear.

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