Jeffboat

The props we used for our first trial were Merc 18" x 32" pitch 5 blade. They pulled 3450 rpm and the boat did 11 knots! We fitted 2" spacers and got the same results.
This was all done with CMD aboard.
This is a boat we have previously supplied with Yanmar/ASDi8, 1.28:1 and acheived 57 knots.The props for the Arneson were supplied by Rolla, 20" diameter x 27" pitch 5 blade. Rolla say we need 22" diameter to make 1.35 to work! They recomend an 18" for the 1.15:1. We have a pair of 6 blade 18" x 30" coming to try with the new drives.
Video of the arneson boat here; http://www.youtube.com/user/HuntonGe.../0/iOOOMj-pK5w.

HabanaJoe

Jeffboat - the video is very cool, nice boat! Did not realize it was more of a crusier than a go fast but that doesn't change much.

Here's the problem with what Rolla wants you to do in getting 22" props in my opinion - you have the little B series engine 5.9L as as you keep increasing dia with the surface props the drag the props have when fully submerged gets to be soooo great you simpley do not have enough cubic inches to make enough low end Hp to break those things loose (I know vent tubes, etc) and if you do because of lower gearing then you won't have enough RPM available to compensate to make the speed.

The dia as far as I'm concerned is strictly to develope ft/lbs of thrust which has no bearing on speed at all. Speed is from pitch - distance traveled. But as you increased dia to make a prop more effiecent at slower RPM you then need to increase the pitch to overcome the loss in prop speed and pretty soon you have a tug boat propeller - lots of thrust no speed.

I 100% agree with 18" dia and 1.15 gears, we ran close to that set-up in 1990 (20 years ago) and you can run into the low 70's no more than that. 17" / 17.5" props 400 hp 1.15 gears, heavy, heavy patrol boat and into the high 60's. With a lighter boat same package up the pitch and you hit 75 mph.

To go faster than that you need prop speed and I say this on here over and over and I will find old pictures from 25 years ago over the next day or two to demostrate that. If you have the Hp and want the boat to go faster you need to go to smaller dia propellers and spin them faster.

Looking at your boat if you get into the 70's with that power you can't ask for much better, it is a big, heavy, sqaure boat not like a 42 Fountain that is low, light and shorter (doesn't make either bad just different)

I assume your problem is you went backwards with the Cummins from where you were at? You wanted to buy a package and not peice together drive, trans & engine?

I would also guess the Yanmar turns a little faster than the Cummins (by the specs) and when you look at prop speed of the Yanmar at 1.28 vs the Cummins at 1.15 they might be very close?

I think you are on the right path, smaller and faster the question is how much and that is trail and error for the most part - just don't let people tell you how BIGGER is better it's bulls**t!

One word of caution, the smaller and faster the props are the more top speed but less cruising speed and you need to be going faster to stay on plane with a big boat like yours - it is a balance.

Rik

You should have stayed with Arnesons.. I am not certain your problems are going to go away merely by changing ratios and dropping your X dimension.

If you, and the boat, were happy with the Arnesons performance why are you changing? I mean Cummins will sell you the motor direct, we can supply you with the gear aft so why change something that is working? I really would like to hear what CMD promised to make the change happen.

HabanaJoe

RIK, I didn't want to say that but yea should have stayed with what worked and just changed the engines.

Wildman_grafix

I am posting these for HabanaJoe.

This is Group 1 of 2

Picture "A"

scan0004 by WIldman Grafix, on Flickr

Picture "B"


scan0002 by WIldman Grafix, on Flickr

Picture "C"


scan0001 by WIldman Grafix, on Flickr

Wildman_grafix

I am posting these for HabanaJoe.

This is Group 2 of 2

Picture "D"


DSCN4058 by WIldman Grafix, on Flickr

Picture "E"


DSCN4059 by WIldman Grafix, on Flickr

Picture "F"


DSCN4060 by WIldman Grafix, on Flickr

HabanaJoe

Thank you! Let's start with the first 3, two pictures show the Malestrom with the speedmaster style lower end for the Sternpower drive and the the third has a Merc style lower (Mirage props).

I'll answer a couple questions first so no one has to ask:

- why SternPower? Seen them on Kurt's boat, ran OK, we are in NJ, they are in NJ and we can run there and get and play with gears as needed.

- why the little steering cylinders? They came standard, first time out testing almost bent one in half, changed that night!

- why the high X-dem? We had up to 4" of spaces so start high and space down as needed, to hard to raise drive

- why bronze props? yes, they flex, yes they don't last but testing when we're cutting them weekly over at S&S and playing and playing, the cost and time for new stainless propellers is to great and too long. Yes, we raced with stainless after we figured out what to do.

History of us, the first diesel boat was the red Monza 24X7 I've posted on here although a good boat, it never broke 60-62 mph with the diesel (250 hp 6.9 then 300hp 7.3). We were not very smart then as to why? We figured when the boat had a 475hp gas engine it went like heck with the same Sternpower drive. We thought just not enough Hp but look at all the torque we had and we put on these big dia propellers it should go like heck. Changed gears faster, slower, pitch, etc, etc - nothing made the big leap we wanted

Maybe the weight of the diesel & drive, etc, etc was too much for the narrow pure deep V hull and it just won't go faster because of these factors - it must be the boat everyone in the boat business can't be wrong like Mercury, Sternpower, the engine builders we talked too other racers and boat builders who shall remain nameless can't all be wrong because they all say the same thing - they have experience we thought- right??? It has to be us.

With that said we ordered the Malestorm, wide beam, flatter bottom, notched transom, pad bottom - everything needed for SPEED!!! We also took everyones advice about how to run a diesel boat, you need BIG, BIG propellers and deep gear reduction.

First time out with the little cylinders and an 18" dia prop but now 375Hp @ 3,600 rpm's - it should fly!!! No, 65 mph. Mind you we had reduction gears in there, I think 1.36 not sure??? ***Sidebar - the big propeller put so much torque on the drive that the moment we got running fast the boat wanted to flip over and one steering cylinder bent like 45 degrees!

Take the propeller down to 17" dia, we picked up a few rpm's and a mph or two. Ok, take it down to 16" and then we hit the governor hard and pick-up another couple mph's - maybe onto something.

Let's change lowers to the Merc style lower and use the Mirage propellers of the day 14 5/8 X 23 or something like that and go to 1:1 gear - a little faster yet but now we hit a wall because the hydrodynamics of that lower sucked and no matter how many rpm's or pitch or anything 68 mph was it and it was taking very little of the 375 Hp to get there (boost gauge was lite) - so back to speedmaster lower and full cleavers.

So, pitch nor dia had much to do with speed, take a 18" x 31" or a 14 5/8" X 23" and we can go equally as fast - kind of disproved what people believed, right?

We knew we had to have prop speed then to get going faster and everyone was wrong that we needed dia because it was a diesel and had more torque that meant nothing - prop speed was king.

In the propeller pictures you see three of the orginal 23 year old bronze cleavers (in house still, why???) with the final and fastest one being only 14" in diameter.

We kept going up in gearing until 1:1 with about 15" in dia and ran high 70's - 80??? at 3550 rpm's on engine speed. that is a special number because look at your gas engines turning 5,500 rpm's and through a 1.5:1 reduction notice the final propeller speed?

We hit a wall that was it no more speed, we kept testing with that boat even after the acquisition by SH but on the QT. The Malestrom now had a 400hp Cummins B in it (the SH's ran the 380 Hp version) but only turned 3,000 rpm, in fact after 2880 rpm the Hp dropped of allot. We started the whole process again of going up in dia because we had more Hp and more torque now - no more speed.

We had the Buzzi race boats there and ran them everyday and could run 95 mph on 14 1/2" propellers - why? I know they turned faster but everyone and I mean everyone that we talked to and many people on here that we hold in high esteem as experts still said Diameter, Diameter, Diameter and that Buzzi was wrong - yet his diesel boats beat the crap out of our US gas boats - could it be that simple. In all honesty people here didn't run diesels nor care about them so I know they spoke from inexperience and just went along with traditional wisdom.

Then we made OD gears for the Sternpower and a set of reverse upper geared TRS drives and all of a sudden the speed!!!! The Malestrom ran OD gears one time, and only one time so we had just about 4,000 rpm's propeller speed and used that little 14" bronze cleaver in the picture and it was over 85 mph with the Cummins 400hp.

Toward the end of that day the drive blew apart and that was that, we imersed ourselves into making the SH engines and developing the patrol packages , etc, etc and now an OSO member has that same Malestrom out in CA except all white!

That is how I know without hesitation it works and Buzzi was right not wrong! If I said who I brought countless gin & tonics for at the races and tried to pick his brain only to realize he's not that well rounded you would be schocked by it - people don't understand Hp is Hp, it is a unit of work and a propeller does not care what drives it, it just needs to be able to turn in the rpm range it works best at.

Oh, the drive height, made little difference, up, down, left, right, you can argue that it made 2 mph more or less - for our purposes of breaking through the 65-70 mph barrier. Yes, it made huge differences in ability to trim the boat but speed - not really.

If you have to work that hard at it, you have something fundamentally wrong, we didn't need tweaks we needed leaps!

THERUSH

Hey Joe,

What are your thoughts on the 480 Cummins in your old SH with the green engines and ASD-8's ???

HabanaJoe

You mean the 380 Hp B's or the C's because the Green engines were only 380Hp on the dyno?

Not to be funny but thoughts on what, how to go faster, what are you asking me to comment on?

Rush you should be racing that boat in the around LI or some of the races charlie is planning, it would give people a run for their money!

THERUSH

Sorry Joe,

Didn't mean to set you up but I am in the middle of repowereing With 480 QSB Cummins. Just been a long process with other business commitments. I am keeping the ASD's but switched to electric shift TD gears (same 1.15 ratio).

Not sure where it started life but it has the green 5.9B motors (at least under the paint) I got it from LOTO about 6 years ago.

I am with you on prop speed and HP vs torque just curious if you have any thoughts on the upgrade.

Rich