Prop. Hub

[Danielsan]

Hi there, in a general way what is the apprx outer dimension of an prop hub say in a duoprop setup?

Just need to know as I designed a prop strut with an diameter of 100mm

are there some sites where to find dimensions etc around props?

thx,

[marshmat]

The dimensions of a prop hub vary greatly depending on the type, diameter and pitch of the prop, and whether exhaust is run through the drive or not.

You say you've designed a prop strut with 100mm diameter? and yet you mention a duoprop (coaxial counter-rotating) setup? Coaxial counter-rotation is amost exclusively a sterndrive thing, it's not really suited to single shaft drive. Can you elaborate on what you're planning?

Any prop manufacturer worth their salt will list available prop sizes on their website, or with a quick phone call. Try Google or the YellowPages for dealers in your area.

[Danielsan]

THX Marshmat,

I found a ?simplified? way (good or not, who will tell?) to use dual counter rotating prop on a single shaft.

Did this because I tought if a stern duoprop has some improvement in eficiency, why wouldn't a single shaft have one with this setup?

The propsizes are found easely, but the hub is never mentioned. I know there are different makes but in general they are around 70-80mm in diameter I tought, this why my question. It has to be a prop as used with the sterndrive duoprop setups.

I do this because I love mechanics and making things by myself (cheaper) good or bad, one has to learn ;-)

greetz,

[fcfc]

beware. propeller efficiency is one thing, overall efficiency is another one.
If you win 5 % efficiency propeller efficiency going duoprop, and loose 6% in mechanical losses, I would call this a unfair deal.
The same one as spending 5 000 eur in engine parts and work hours etc ... to save 2 000 eur on fuel bills. Only this of course if the savings are not flushed by the first assistance cost for a failure at sea ...

The best way I have found to limit spending in a boat is not to go hi tech, it is pitily going smaller and slower.

Now, machining can also be a pleasure. And you can enjoy designing and building your own contraprop system.

[Danielsan]

I must say I am getting more and more confused.

I have allways since I was 5y young dreamt of having a boat now 24y later
I think I will manage to make this dream real. Though I have not the money to buy a new nor 2nd hand. I would like to systematicly pour in some money and make it a 2 year project and do the Hull myself.

All came upon seeing 1 1/2 year ago a real car engine in a small boat... :?:

since then everything started, viewing, sketching, searching,...

then I came on this wonderfull site. But since then everyting started to complicate.
HULL: Male plug, female mold, building directly on the plug, RTM,...
ENGINE: Car engine, Boat engine, Bus engine, Truck Engine,....
PROPULSION: Direct drive, gearbox, V-drive, Sterndrive, Jet drive, surface drive,...
Considering all this things over and on and on and on, back an forth and getting more and more :confused: :confused:

All I wanted to do is make something a bit trendy, seaworthy, to spend some time with wife and kids at a reasonable price.

This site made me open my eyes, maybe a bit to much.

As I said I love mechanics and sometimes I see that we(the company for which I work) designed some comparable pieces, nothing to do with marine apps, we made them for a fraction of the prices handled by the big names, so this upsets me a bit.
This Is also the reason for me sketching and trying to get some other ideas on how to do things, searching for info,...

[fcfc]

A funny site for an unaffordable boat.
http://www.setsail.com/dashew/progress.html

What is funny is that they started building the boat in end september 2003.
By march 2004, the boat left the metal boatbuider. hull, deck & roof done. to go to the finishing boatbuilder. At that time, the finishing boatbuilder had already started prefabricating furnitures. And then it took from march 2004 to may 2005 to "finish" the boat.

6 month for the hull. more than 15 month for the remainder. (furnitures prefabrication started while still metalworking).

You are focused on the hull and the propulsion system. But how is the cost of a fresh water system. Water tank/ grey tank / fittings / non smell pipes/ pressure pump / sump pump (shower) / water heater for a family to spend some holiday time aboard. How about a fridge system that does not force you to go shopping or restaurant every day at the marina ? How about an electrical system that allow you microwave oven use and does not force you to run the engine 5 hours a day. How for a mere watertigth deck hatch and some opening portlights to simply get some air and ligth. How for engine soundproofing and wet exhaust system.

BTW, unless you build a cargo, you will no longer find any true marine engine. All are car/tractor/construction equipment/small truck/truck engines converted for marine use.

[Danielsan]

Indeed all the rest interior, plumbing, electrical,... even not mentioned...

In the first case I will have a bare boat Hull Engine steering prop electrics, the rest will come later ;)

Electr(on)ics won't be that big of a deal :?: , as I am working as an engineer in an engineering company, mechanical and electronical.

What kind of experience do you have in boatbuilding?

greetz,

[fcfc]

None. I have never built a boat.

Only helped or met a few homebuilders. Had at that time access to a small woodworking workshop. Furnitures, not boat or even marine.

One was a ferrocement ketch. No help. Just heard and saw the story. After building the bare hull, the builder put it afloat. The bare hull without any equipement or ballast floated right in its lines. He took the hard decision to sink the hull and sell the equipement he had already accumulated.
Second built a small cold molded ketch. Modified the original design to have smaller berth for his two babies. When the boat was ready to sail, was not a problem because his childs were old enough to have their own life and no longer sail with him. Right size for his grand childs.
Third was a steel sail boat. Correctly terminated but had the extreme luck to work in a technical school where other teachers, specially steel forming (fr:chaudronnerie) teachers , were also amateur race sailors and helped him with knowledge AND professional tooling borrowed from the school. Correct stem forming and welding was at that price. ( Not exactly developable)
Last one was a fiberglass sail catamaran. kind of asymetrical. For layering and glassing the first hull, a bunch of people with more seesigthing and willingness than knowledge came. That resulted in a more or less average hull. For the second hull, only a few motivated and knowledgable people came helping. That resulted in a really better and ligther hull.

My tough is that homebuilding a boat can be done. But homebuilding a boat that will keep a decent resale value 5 - 10 years after its launch date (not start construction date) is a very very very hard job. At the opposite, the current market price for a 30 year old grand banks is the ballpark of 10 time the original purchase price.

[Danielsan]

This encourages me alot? ;-)

[fcfc]

Just transpose your boat dream to car world.

Sure BMW are fines cars. You cannot afford a new one, not even a used one. But BMW cars are only point welded formed steel sheets, aluminum and kind of plastic castings, and a few steel machined parts. From the price of raw materials, BMW are very very expensives. So you are telling I can build one in my garage for less than the price of a used one.

Would you trust someone telling that above ?


And then, sure there are homebuilt cars. And even less expensive than a used BMW. But they simply look much more like sandrails, buggies or WWII Jeeps. And the probability they ran as fast and as long as BMW with the same failure rate (or lack of) is rather low.

Not forgetting too there are a bunch of used cars less expensives than a used BMW.

Now, go back to boats.
You cannot (today... tomorrow is another day) afford your dream boat. Building it in your garage is dubious. But there is a bunch of used boats or other homebuilt designs *within* your reach. And you will enjoy them for real. They will simply be a bit different from what you initially dreamed.

[Danielsan]

It ecourages me even more??

It happens that my first car was a BMW I got from my father in a dubious condition. I worked a lot to get it on the road again. Later on I bought myself a BMW 633CSI and we rebuilt I quite good. To compare prices the BMW 633CSI must have cost around 50-70.000 EUR new, the thing whe bought was around 1.000 EUR.
Traduce this to a boat, say daycruiser, Bayliner - Real,... new price 60.000 to 100.000EUR, 2nd hand it goes 20.000EUR and more upon age and condition, hence the difference?
I can put in a good running engine in my BMW 200HP for 1500EUR but I cant find a good running engine for a boat for less then 2500EUR.

The marine exclusivity pushes these prices up and up and up.

I must say I got somewhat out off my thread but it's nice to exchange points of view.

Further on I must say that I have seen preety results from homebuilders, that I prefer above the commercial models of the big ones.

A nice initiative of a Dutch company providing nice kits for nice models I found on
http://www.dolphinsboats.com c'est pas en francais mais faut aller voir chez "bouwers"
there is one model that is completely finished of the designers themselves. appx. 60 models have been sold last year and are being homebuilt now. Shure you will see difference in finish but they are homebuilt.

If I could have same results I would be more than happy

a+

[fcfc]

I fear you are confusing things. There is a development cost : the cost involved up to the first correct prototype. And then a production cost : the cost to produce a model identical to the first correct prototype.

Building from a kit does not involve development. Only production. The kit price only cover a part of developemnt. Depending on how many the manufacturer intended to sell. If it planned to recover costs on 10 kits, kit price for a customer only include 10% of the development cost.

Now, if you build one only from scratch, you will have to cover 100% of development cost. May not be the same thing.

If you build your dream boat, you will not be in the situation of a kit buyer, you will be in the situation of the kit producer, but with 0 kit sold.

I bet his first correct prototype costed way more than an equivalent production boat. How many scrap pieces did he produced and tried before anyone could assemble his parts with a reasonnable success ? How many tooling (cnc cutting etc ..) and marine engeenering he had access. This was certainly not the first boat he build.

[Danielsan]

no indeed, the designer works for pantera yachts in the netherlands and has also designed the AR-Yacht so this aren't his first ones. But the kits you see are all first off.
They are two one designer and one sales I think they do a fine job.
As for myself I dont take into count my personal time I spend digging and thinking. The only thing I will do first is when hulldesign is copletely finished export the stations do dxf 1:1 scale them 1:10 have these CNC cut to see if it can be put togheter in a scale model. Next thing will be "eventual (read lots)" modifications. taking the 1:1 stations have them nested and CNC cut. need approx 13 multiplex plates 120x240cm at around 40EUR per plate.

We are way off my initial thread :cool:
greetz

[artemis]

Indeed, we are way off your original thread. But to go a bit further... It sounds like you have not selected a hull yet, or have you? If you haven't, have you made a list of what you want... take the family for a month cruise? :) take yourself and a friend for an afternoon of beer drinking and fishing? :D take an afternoon to lazily move along a 10kph? :) take an hour to pound your kidneys out and go 60kph? :eek: If you can post a list, I may be able to direct you (as I'm sure many others on this forum can) to some exisiting boat plans that you can use.

[Danielsan]

I think after a few redesigns, I came to my as good as final model. It's nothing new I know, but this is the first one hopefully not the last

should be something like a planing hull? would put in a 265HP diesel engine,...

[rxcomposite]

Daniel,
Before you embark on your duoprop project, read the principles of Naval Architecture. There are three more variants to these.

The freewheeling second prop (like in turbine design).
The fixed nozzle.
The Hull (prop) stabilizer? the correct terms escapes me at the moment.

Boatbuilding may range from simple to highly sophisticated. This forum attracts the best minds in the industry and i myself find that i learn from them. If you are new to boatbuilding you will have a tendency to be confused as the boats and the technology is so overwhelming.

It is a lifelong experience that many shares in this forum. Take things easy, enjoy building the boat, and balance your experiments. Build one boat, use a lot of elbow grease and beer money, and be ready to takle another one as the bug will bite you.
Rx

[cyclops]

The usual purpose of contrarotating props is when you have so much horsepower to be used, that the prop diameter is too large to for the available space provided. The additional geartrains and bearings waste about 25% to 30% of the running horsepower due to frictional gear losses. Double Herring Bone gears can help. Still, it points up a basically poor design that was over powered for some reason. The best example of a need for contra-prop was the British aircraft carrier version of the WW II Spitfire. 2 props of 5 blades each so the props would just clear the deck on landing. Bad extreme design.