Trimax and Arneson comparison

[PetterM]

Does anyone any direct comparison data between these drives? Have anyone fitted these drives to the same boat. Especially interested in behaviour during acceleration (around hump) and steering at low speed and intermediate speed, and high speed.

[PetterM]

I suppose this question could be generalised as pos and cons of fixed vs. articulated surface drives. Any takers?

[Steve H]

I converted my 42 Harley from fixed surace drives to Arnesons. So I guess I could answer any questions related to that specific conversion.

Steve

[PetterM]

Would be great if you could help me with the following:
I am interested how to two compares during:
Low speed manoeuvring
Steering at low planing speeds (just over hump speed)
High speed steering
Acceleration.

..and:
Minimum planing speed?
Maximum speed?
What power are you running?
Why did you convert?

Thanks for your help...

[Steve H]

Would be great if you could help me with the following:
I am interested how to two compares during:
Low speed manoeuvring
Steering at low planing speeds (just over hump speed)
High speed steering
Acceleration.

..and:
Minimum planing speed?
Maximum speed?
What power are you running?
Why did you convert?

Thanks for your help...

Low speed, as in dock handling? This was the main reason for the swap. It was a nightmare in a crowded marina on a windy day. It is night and day better around the dock. It handles as well as a inboard/outboard if not better.

Low planing speed steering (just over the hump) is a little better, it wasn't that bad before.

High speed steering is much better. The boat still has bow steer issues, but near as bad as with the fixed drives. (I'm still playing with props)

Acceleration is about the same when light on fuel (100 to 200 gallons), but much better with heavy fuel. (400 to 600 gallons)


Minmum planing speed if light is under 20 mph now. That is down about 5mph from before the drive swap. I must mention here that I am large using K-Planes with even larger stainless extension bolted to them. These make a huge difference.

Max speed is about the same as before which is 48 to 50mph.

I am running twin 415hp 502's. Twin disc 1:5to1 trans. 18X21 three blade old style Rollas.

Why did I convert? Dock handling mainly. Boredom too. Seems like I always have too many irons in the fire. But if I knew how much work it was going to be I would have just installed a bow and stern thruster!

[PetterM]

Thanks for your helpful replay! You have given me plenty to think about.
Could changing the propeller rotation help you bow steer problem?

[Steve H]

Thanks for your helpful replay! You have given me plenty to think about.
Could changing the propeller rotation help you bow steer problem?

Props are currently turning in. I am reasonably sure that reversing them would make it much worse.

[Rik]

The Arneson will be an easier cleaner install and will work better for all around boat use.

The tri max will require hull changes to install and will not accelerate as well nor handle the different weight load changes.

[PetterM]

I read somewhere that in high speed turns Arneson drive is more likely spin out than a fixed drive. Is this a factual? If so what’s the mechanism for making this happen?

[Steve H]

I read somewhere that in high speed turns Arneson drive is more likely spin out than a fixed drive. Is this a factual? If so what’s the mechanism for making this happen?

News to me. Maybe in a full race application? But those boats spin out all the time no matter if they have surface drives or not. It is usually due to operator error or a broken steering component.

Remember: Anything that you read on the internet should be taken with a grain of salt. Especially when it comes to surface drives and this website. I did alot of research before I converted my boat to Arneson's. Most of the "advice" I got was false, kind of like urban legends. Someone starts a rumor then it gets repeated enough that it becomes fact.

[Rik]

I read somewhere that in high speed turns Arneson drive is more likely spin out than a fixed drive. Is this a factual? If so what’s the mechanism for making this happen?

Probably a rumor started by Fabio

[Steve H]

Probably a rumor started by Fabio


Exactly:)

[PetterM]

Fabio spreading rumours again hehe...and I thought he was to busy getting is boat ready for the around Britain race…I do agree that there are loads of people on this site with a hidden agenda; some even use this site to slander the competition…that beside though, one can still learn a lot from people at this site.
With regards to the Arneson spin out scenario, after thinking about it, I suppose what I was getting at was if one has a twin set-up, then in a turn the turning moment is achieved by the composite effect of both the rotation of the skeg (rudder effect) and rotation of the thrust force. Looking on from the back in a turn, the outboard propeller disc is moving towards the centre line of the boat, so that the wetted (working) swept area of the propeller is decreasing, and therefore thrust is reducing. The effect will be opposite on the inboard propeller in a turn where thrust will increase. Obviously in a turn if the outboard thrust vector is decreasing and the inboard thrust vector is increasing this will reduce the turning moment…So I was wondering if on a very fast boat this could result in a spin out? Maybe I should try to calculate the propeller forces to find out… :confused:

[Rik]

The propeller rotation can be either inboard or outboard depending upon what the boat likes best.

This is the same for any propulsion not just Arneson.

Now if the boat is being steered by the vectored thrust as well as the rudder on the Arneson, there is in fact more control and less wheel input needed to achieve the turn resulting in less steering arc needed to accomplish the turn.

As the boat list into the turn (assuming the boat does not want to roll outward at this speed of the turn) the relation of thrust of the outboard propeller in relation to the inboard propeller thrust will depend upon the deadrise of the boat at the stern, the displacement of the vessel and the distance of the propellers in relation to one another.

Now you mentioned the hypnosis on a very fast boat, (relative statement) and how this would affect the situation.

Mind you on a very fast boat, the propeller submergence on an Arneson is the same relative submergence as on an I/O and even a fixed surface drive.

Now for a high speed turn your hypothesis of the inboard propeller thrust being able to overcome the directional thrust of both propellers as well as the resistance of the rudder forces in the turn which will in turn make the boat turn the opposite direction than the steering of the drives is nearly impossible.

I would liken this to a hypnosis to a boat going forward and hitting a wave off center casing the boat to list to one side and the highest propeller would then loose thrust (assuming the propellers are far enough apart to make a difference) and the lower propeller would then make the boat hook port or stb.

Mind you, this hypnosis is valid on a fixed surface drive, an Arneson, even an I/O as the submergence of the propellers below the keel is less than the height of the waves in which the boat is running.

Not a very practical hypnosis and not reality as seen in the current flock of high speed boats. They all seem to keep going straight in the cross seas and the Arneson propelled boats do not seem to be spinning out in the turns.

[PetterM]

Rik thanks for your comments, do you by any chance work for Arneson? I wasn’t trying to have a dig at Arneson in any way shape or form, just so that’s clear. It’s commercial success speaks for it self.
I am still a bit intrigued by the high speed spin out issue, be it with fixed or articulated surface drives. From what I have seen on videos etc it may happing with the boat going in a strait line at close to top speed. Is this a propeller issue? Or can it be caused by sudden change in propeller speed?
Here an expemple (on a surface drive with rudder steering) http://www.youtube.com/watch?v=VNjEnDdlMoA ca 3:30 into the film.

[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?image=29876_Copy_of_B4_Pic_1c_Rear_122_443lo.JPG

http://img40.imagevenue.com/img.php?image=29881_Copy_of_PC180084_122_20lo.JPG

http://img14.imagevenue.com/img.php?image=29887_P1090009_122_177lo.JPG

http://img172.imagevenue.com/img.php?image=29892_Copy_of_rudders_off_for_transport_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