Trimax and Arneson comparison

[Rik]

That is the "Metamarine" hull with the Metamarine copy of the fixed Arneson with rudder steering.

That hull has a known issue doing this exact same thing as you see in the video. Last year they spun a 360 degree and kept going. Scary ride. Different race as last year they were side by side and it looked like they hit the other boat when the boat turned on its axis.

What is not shown in the video as these two boats are coming together is that they are setting up for a turn at the buoy. The boat lays the nose down and the wetted surface area hooks the front (called bow steer) and around it came.

They simply might not have a deep enough rudder as this is a race boat and they might be trading off stability of speed.

They might have dropped the trim tabs too much or the CG might be too far forward in the boat. It started with a turn of the rudder that much is about all that is known for certain.

[brunello]

It is fairly obvious to me that there is no 'right' or 'wrong' drive as there is not a 'best' propeller or hull shape, if one is not looking at a specific application. Provided we are speaking of properly engineered & designed stuff, the only problem is to properly select and match the main parameters. Hull shape and it's balance, craft mission and its scenario, power to weight ratio and how power and torque are delivered, the drive's characteristics and obviously the propeller's design, use of tabs and power trim and even driver's skills or peculiarities, are only some of the variables that a BOAT DESIGNER should try and balance for optimum result. We should all try and avoid becoming maniacs, since probably the worst thing about surface drives is how many people - all stating that this is a great propulsion principle - are fighting one against the other, not only in order to state that surface drive "A" is the best in the world but, especially, insulting somebody else system. The final result is that other people (not devoted to surface propulsion), more industrially an practically minded, works hard to improve their products, get great results and in fact sell more drives. There is a lot of work to be done and surface propulsion has not managed, to date, to show its full potential. Even in flat out race boats (not the most difficult kind of boats to design at all, simply because at least the goal and design mode is reasonably well defined), there are different ideas. Look at P1 racing: in 2006 a Donzi retrofitted with a Flexidrive Speed Drive System (fixed steering, single rudder aft, my design) won the world championship, after dominating all season. Last year, a Fountain with Arneson's (no presentation needed) won the championship, most convincingly. This year, too early to speak about final results, but a brand new (and perhaps 'young') Cigarette fitted with Mercury 6 drives (a stern drive, but fully converted to the surface drive philosophy) is almost invariably in the lead for the first laps (and yesterday won in Tunisi). Personally, I much prefer a fixed drive (no steering) with the rudder well aft, and also like to work upon the rooster tail; but I would never (today, I did in the past) speak against Arneson's or Mercury's, since they are real alternatives, of outstanding quality, simply with a different approach. Also, no need to reply to offensive statements about one's genuine work. I have seen many raceboats spinning-out and the drives were not the single variable involved. It all depends on the application and the overall package. You don't just stick a drive on the transom and get 'the best' or 'the worst' and it is no coincidence that 'Fabio' has won so much when he designed the entire boat - often even throttling it.

[Rik]

True. The biggest sin is the ignorance of others and the rumors they can spread.

The Cigarette boat, which was built by Skater Powerboats, runs well with the supercharged engines. This year in P1 every dog has his day so to speak.

Carr had pole position but they are fighting mechanical gremlins from the sinking of the boat at the start of the season. They should have gutted the boat and rewired it but time was working against them.

OL had one race that they shined very well at.

FWW has been there all year but lately has seen some bad luck lately. I think they will triumph again this year as in last.

Buzzi was good when he had and built a competitive advantage for himself. He was racing 1200 hp diesels against 700 gas engines. Did anyone really expect any less?

[ChrisN67]

Hi folks,

I have an Interpid 339 WA with twin Yanmar 6ly2's. SBM surface drives and Rolla 18.5 x 25 5 bladed props.

I test drove the boat , bought it, then stripped it. I really did not get much time to look things over as well as I should have; but one thing I rememeber was that the boat seemed to run bow low.

Does anyone have a recommendation regarding the more desired rotation of the props to increase bow lift?

How about a rocker in the last 3-4 feet?

Thanks

[PetterM]

Which way are your props turning?
Do you know how much rake your props have?

[ChrisN67]

They swing outboard, and with regards to the rake, I am not sure. I posted pictures of the props and the drives here:


http://img24.imagevenue.com/img.php?..._122_443lo.JPG

http://img40.imagevenue.com/img.php?...4_122_20lo.JPG

http://img14.imagevenue.com/img.php?..._122_177lo.JPG

http://img172.imagevenue.com/img.php..._122_600lo.JPG


I only took one ride in the boat prior to reworking the drivetrain and structural components.

[PetterM]

Good looking boat.
First thing I would try would be to change the propeller rotation to inwards turning.

[ChrisN67]

Thank you, I have totally reworked her to include complete engine overhaul, transmission, drives, engine bay, transom, electronics, and of coarse upholstery.....

From the pictures shown, is there a way to determine if i can get the stern to settle and get a higher angle of attack?

I am reworking the last 6 feet of the boat and I was thinking giving the hull a slight rocker.

Any ideas? I am betting this is something that requires a supercomputer and 40 naval engineers to crunch the numbers, or just prudent guidelines and trial and error.

[PetterM]

If you have the opportunity I would recommend that you make a small step in the hull rather than adding rocker.

[f250]

This summer i had the chance to go on a test run on a perching 56 with arnesons.
They did some u turns en some 8's at 40 kn.
Nothing wrong with the steering amazing boats, just af to win loterie.

sorry for the bad english