diy surface drive?

Rik: I understand that you want to promote your product, but it is complicated and not too appropriate for use by non-professionals. Arneson drives that stay in the water have seal failures from barnacles and other growth among other problems.

 

Unlike a sterndrive, if the boot fails on an arneson it is not a problem. I don't know one boater who switched to arneson who switched back. I don't let barnacles grow on my boat. I keep it clean.

 

Rik promotes arneson and you promote cal500 (which doesn't trim)

At least Rik doesn't hide who he is promoting.

 

Oh noo... I merely asked where you get this information from? Your intent to deflect and avoid answering the question at hand while continiouing to make outrageos claims is perplexing. It only concerns me when someone starts to believe your mistruths as facts.

If you wish to promote the Cal 500 or whatever, here's a tip. :idearomote on what you have of value and avoid spreading mistruths about others in an attempt to make yourself look good as currently your experience or lack thereof makes you look :?::?::?::?:

 

I agree.... If the package is capable of 35 knts +, the drives should be trimable. Also, the old Arnesons used to suffer from lack of bow lift. Now, the new 20 deg rake props have helped solve this problem. Back in the day we put a set of arnesons in a 38 cig. The boat did not have the bow lift and was always stuffed..... On a side note, most of the 200mph cats run the BPM surface drives, they of course, are trimable. Also, just because I don't have over 7,000 posts does not mean I don't know what I'm talking about. I prefer to spend my time in the shop, not on the computer.....
Thanks

 

If the package is capable of 35 Kts or more they should trim!!! Well there a snippet of information I had not heard before and makes sense. That should throw some light on the trim-non trim debate. Non of our Gurus on the Forum brought that up before.

I have fixed 24x24 with pops sited 16inch from the transom , I need no ventilation and can hit 3000 RP in the marina if I wanted to, but then ide have to try to stop 14 tons.

Ive never felt the need to trim at my max speed of 24KTS. Twin 250HP with Hurth 630 A down 8 degree driving 2 inch shaft on 4 blade nibrals cleavers by Seafury.

( Factory boat is conventional with 300 twin and 24 KTS max.)

I reckon I'm in the 10% increase in efficiency they talk about.

Incidentally I told Seafury what boat I had and what I wanted they told me what engine G/ box and props to use.

If you buy a boat then an engine and a G/box and then ask what prop to use , they wont like you very much.

 

Well, I didn't want to get into this one but since I have experience with assembling, out drive, outboard, jet, air drive, V drive, straight drive, and surface drive boats here is my 2 pesos:
1. You trim an out drive to "air" out the hull and reduce friction.
2. The same for an outboard. You also use a jack plate to reduce the drag of the foot or gearbox in the water.
3. You trim jets to lift the bow too for the same reasons.
4. My own experience found that air boats work best with the thrust line parallel to the keel.
5. V drive and straight shaft boats only benefit from trim tabs to improve take off and level the boat.
6. Now we come to surface drives. They are unique. When parallel to the bottom, they are almost clear of the water. So they only work in a down angle range. Therefore the drive will not lift the bow. All lift is provided by either an air entrapment hull or that the machinery, fuel and equipment is biased to the stern. The reason for the trim is so that a large pitch and surface area prop can be used. The boat is generally highly powered to get the boat on a plane. Once there, the prop is lifted to decrease the amount of blade hitting the water. This allows the RPM and the power to increase driving up the speed of the boat. Believe me when I say this: the hardest thing for a fixed angle surface drive to do is plane.

 

The Sea Sleds were very successful with surface drives that were not trimmable. I think that a bit of trim can be useful for fine adjustments. However, it is often used to try to fix a bad design or installation.

 

Albert Hickman's boats ran very large engines - engines that could run a 3 point hydro over 100 MPH. Albert's boats did about 60 MPH. He was so preoccupied with drag that his rudders were flaps that tucked into the stern. His hull design had a wide flat stern to help with planing. His props were wide "elephant ear" props for grip during transition to plane. These same characteristics doomed its top speed.
Aircraft can't alter prop diameters and they could not lift a load until they invented the controllable pitch prop. Surface drives can't alter pitch but they can alter how much prop diameter is in the water which amounts to the same result.
I also note that Hickman sea sleds are no longer sold...

 

This is correct, the trim van be altered by the rake of the prop.

In surface drives you swing the biggest prop you can get on because when planing you have only half of that in the water.

When set up correctly and ventilated a fixed planes easily. I have one!

 

So only perfect installations or perfect designs lend themselves to a fixed surface drive. How does one find the perfect boat? Is this like finding the perfect women?

 

In responce to Arneson drives being $$$$$$$$$. Before I built my hydro, I had (and still do) a "cocktail napkin design" of an Arneson style built with auto parts from a wrecking yard. A gimble would be made from a front axle and hub of a front wheel drive car. I bought the "yard" parts for a future project. I would have gone with this set up first, but I wanted the hydro first, vee bottom later.

 

Rake only moves the thrust point further back from the stern and allows changes to trim to be more effective. V-drives, straight shaft drives and ships do not usually have rake on theirprops.
The Arneson set up results in a heavy stern. The trim on this design is limited and will only lower the bow. as you cannot put positive trim on the shaft line because the shaft is above the water at speed. An in/out drive prop shaft is immersed and therefore the prop shaft can be trimmed above the parallel point to the surface.
Those who strive for simplicity and purity of design must put up with the drawbacks. Early performance sports cars were simple and could hug the road and corner well but on a long trip they rattled your teeth. Now performance cars have adjustable suspensions. Likewise boats. On a stormy day you can trim the bow down to pierce waves for a more comfortable ride so that the perfect woman passenger will continue to not ***** at you and remain "perfect". You want simplicity? Leave the "perfect woman" at home
Good hulls get better when there is more adjustment possible in the propulsion equipment. Poor hulls do not.

 

Rik is 100% correct regarding the trim on surface drives (Much as I hate to agree with a competitor ;-) ). There are many instances where trimmable drives become a necessity. Surface drives do nothing that is magic, whether France Helices or Arneson. All surface drives apply force to counteract another force. By changing the direction of that force through trim adjustments, you gain efficiency and reduce resistance. It is physics, plain and simple.

 

The travel of trim can not exceed the radius of the propellor, infact far less.

This is miniscule and pointless.

An outboard trims completely different.

If you have a 24inch prop you cant even trim up 12 inches, on a 3 foot shaft what angle is the change of the prop thrust, ----its nothing.

The only thing your trimming is the bite or should I say adjust it. A properly placed prop needs no such adjustment.

A trimmable shaft allows for airiataion of the prop to get slip ,RPM and HP

On a deep V with a 3 foot long shaft thats difficult, but with prop closer to the hull and exhaust ventilation it improves drastically.