direct surface drive questions

I have? Where do you get this information from especially the bit about fixed drive owners being unhappy with them.

You are all living in the past --Surface drives are no longer screeming high RPM racers. Low ratios and and higher pitch are the norm.

To suggest they are noisy is ridiculous and to suggest Kamen did not know the difference between aeriation and cavitation is bonkers.

You should read it again.

Such mystery and confusion of over surface drives!! you need to understand the propeller which is not a screw. Moving the prop up and down does not trim the boat.

 

You are still spewing this B.S.!

How fast is your creation? I might be wrong but I think your build is fairly slow and thus has little relevance in relation to "All Surface Drives"

Once you actually use all the forms of surface drives then maybe your opinion will have more weight but so far your ignorance out weighs your experience. You looked to build something yourself that was cheap, unfortunately you did not create good, cheap nor fast much less professional.

 

Thanks for the pointless insults, perhaps your posts might have more relevance if it held some mechanical explanation in keeping with you position at Arneson.

My unprofessional build will attain a higher speed than that of the conventional propulsion system fitted by the manufacturers even though I use 100 Hp less.

The Seafury propeller of your competitor is hardy cheap.

Perhaps you may want to destroy this thread too with silly pictures of boats with girls on them which you seem to know a lot more about.

Its a shame you are like this Rik and its a shame you don't communicate in a better manner, a little less condescending perhaps.

 

Rik you got me thinking. How much is a pair of Arnesons these days.

A pair of the smaller ones for 250HP with say 26x26 nibral props and all hydraulics --the full monty bolt in.

What would be the weight of one system complete with prop.

 

pretty childish and unprofessional post for a company representative. if you want to attack people it might be wise to leave the signature off.

 

i should clarify the above post. when someone in your position replys rik, layman like myself would prefer to read your technical response to each statement you think is wrong.

 

Frosty, you are the one that makes continious vague unsubstantiated claims that you have never proven, have no experience with, and you continue to do so with a smirk of ignorance. Please note, ignorance is not an insult, rather a term for lack of knowledge.

Rather than try and tear others down with fallacious statements you could have posted your first hand experiences but you decided to go the negative route again and once again rather than substantiate the claims with evidence or facts you distract by speaking of women...

As to cost of others, I have not idea? Propellers cost what they cost. Unfortunately, I've yet to meet a propeller company making them that can hit it out of the ball park with regards to cost and performance. It is a "black magic art" even with the computer models. We all want something for less and they all want more for the same. It's how the world works be that good or be that bad.

As to your creation, have you put an actual "real world" value on your time, effort and energy? As to say, barring the attractive third world labor cost, what would it have cost you if you had performed the same task in your native UK? I believe the disparity shrinks....

 

No not really. I find it worth the effort and risk to dispel disbelief and ignorance in order to remind people that not everyone should be held in such high regards that their opinion is to be taken as fact which could influence they perceptions and decisions.

Just because it is written on the internet does not make it a fact.

Mr. Frosty is more talented than most evident by his creations, but his bias is led by his finances rather than the quality of his options.

 

This thread tends to turn into a mudslinging contest regarding the pro's and cons of shaft configurations, thus hiding the original question; sad! Before it goes down the sink, lets turn back to the original questions:

Frosty has correctly pointed out some important facts about SP propellers; they are a different breed of cat, and you must understand the working principle to get it right! It has nothing to do with if the shaft is articulating or fixed, so Rik's comments are out of context here!

To answer the threadstarters question we must come up with a few numbers, based on the figures at hand. First the speed estimation (40+ knots) is totally unrealistic with the weight/power ratio shown. A realistic speed would be 28 to 30 knots with a total weight of 1600 kg (1350 kg boat + fuel + crew).

Second, the SP propeller can only carry a certain thrust load per effective propeller disc area (just as any propeller!). This loading pressure is the limiting factor, and in order to get over the hump and to be efficient at full speed, you need roughly 17" diameter with a shaft spinning at ~2200 rpm. Obviously that necessitates a gearing of some sort.

Third, if you persist in running this rig with a straight shaft at engine speed, the whole propeller disc has to be working, i.e. fully submerged. Even then it will be working with a high pressure (because of the small diameter), reducing its efficiency, but it is doable. You will have a partially cavitating prop, but if you take a look at the ski-boaters, you will find that they often run direct drive (although with a reverse of course).

Summing up: NO you cannot get a direct drive SP prop to work here, but YES it is absolutely an option with correct dia and shaft revs, and NO, you cannot get 40+ knots with the weight/power ratio you have, and NO, its not wise to go boating without a reverse function.

 

'displacing 1350kg' is what I originally said, as in including crew and fuel etc. That gives something like 9.3kg/hp. I worked for a company a few years ago that built a boat with surface drives that reached 46 knots at 11.5kg/hp so I did not think the 40 knot aim was totally unrealistic. Online speed calculators I have found also backed up the 40 knot speed prediction.

I didn't anticipate too many problems getting onto the plane, with diesel torque and venting exhaust just in front of the prop. Mainly though very light weight for size boats pose little problem in that area in my experience.

 

Ok, that goes in your favour. But only with a decent propulsion efficiency, which requires a far greater propeller disc area than you can get with a direct drive.

 

direct surface drive question

Personally...I would prefer to have the option of simply adjusting a shaft angle rather having to use a gas axe to make adjustments,or even run my shaft drive fully submersed if I did not enjoy boating with just the option of S/P mode. Sea and loading conditions dictate how your boat will perform which is something you can not control at the helm without a trimmable drive.
Some hydroplane setup`s are adjustable using a spanner and a bit of motor adjustment.

 

direct surface drive question

Pics of early development of the World`s First Practical Trimmable Shaft Drive for Boats. Fully soft rubber mounted.Do not need a reverse G/B as twin rudders act like a Kitchen rudder.Run in S/P or fully submersed. Skedge automatically lift drive going into shallows or over logs with a cam like action. Engine power does not need to be reduced for drive to automatically lift.Easy launch or retrieve. Build from High Strength steel or Titanium stabilized Stainless Steel. Single rudder can be used or Dip rudders to completely eliminate drag except in turns. Can be made with a sexy apperance and style.
Very cheap build or Very expensive.No more bent shafts or damaged drive.Go anywhere safely. A home handyman should be able to build a cheap simple model.No need for hydraulics,drive is easily lifted from helm.Home handy man servicing.

 

What on earth are you on? I did not ask you the cost of others anything. My drive system was made in Australia as was the whole boat. Must you comment on total fabrication.

I did ask you the price of an Arneson drive to which it seems you don't know are don't want to tell.

You told me by email 10 years ago that an Areneson would not be suitable for my boat because of the rocker. The boat works fine with the fixed system which is faster than production boats with 100HP less. You had no idea about semi displacement. You sell shiny drives for a quick flash over the lake on a Sunday afternoon, then take it out and wash it and to be honest and Arneson is fine for that but for sea boats such as the Atlantic challenger a more robust agricultural system is required.

Even if I were to want an Arneson again I would not if I had to deal with your none sense.

 

Guys, let’s try to be a bit more polite to one another and get this thread back into a productive discussion.

Thanks very much baeckmo for addressing the original poster’s question again directly.

The secondary broader discussion of fixed vs. trimmable could be a good discussion as well, but let's try and keep the discussion productive and not get weighed down by insulting each other which will go nowhere interesting.