engine horse power

[fredrosse]

It appears that several of we steamboatbuilders think the Mosquito Enterprises machinery (or something of about the same size) would be a good fit to your steamer. The 55 square foot VFT boiler can make enough steam to produce 5 or 6 real horsepower, and if that boiler is forced with a brisk fire 10 or more continuous horsepower would be available. The Mosquito Enterprises tamden compound engine looks about right for your tug also, but a double simple engine would not have the potential starting issues some experience with an engine at TDC or BDC.

You would need to mount a 24 inch diameter x about 24 inch pitch propeller, a prop much smaller would be less efficient, and thus require more power to push the boat.

[georgepatten]

Hello Ron, Thanks for the info, every little bit helps. I would hate to spend a large amount of money and then be bummed out because it was totally inadequate. I plan to remove about two feet from the aft face of the wheelhouse, move the stack forward with a vft boiler directly underneath and engine just aft in the usual fashion. this design will just accommodate a 22"wheel. Hope that's big enough, will experiment with the pitch calculations. George

[DetroiTug]

I plan to remove about two feet from the aft face of the wheelhouse, move the stack forward with a vft boiler directly underneath and engine just aft in the usual fashion.

That is what I was thinking too. I'm not sure how much headroom is in the aft cabin now, but I would leave at least 70". And I would widen the aft cabin and decrease the catwalk width. There is a lot of time spent in around the engine for the engineer, the more room he has the better.

Also, after shopping for second hand props in the 20-22" diameter range (22 is my max), most of them have an 1-3/8 or 1-1/2 taper bore. So go with that size prop shaft. The prop shafts in these are long, I used a 1" and I get twisting and flexing because of it. I have a remedy for it, but it's best to avoid it altogether. Finding a prop that fits the shaft omits the need to make tapered reducing bushings. I need to make one now as I'm putting on a 20 X22 4-blade with a 1.5" bore. Present prop is a 1.375" bore. Just make the shaft out of 304 stainless round bar.

Back to the engine: Iron Chief has the Tiny power twin in it 3+3X4. It's really more engine than needed. It will run a nice cruising speed at 40 psi. And run 7.8 GPS mph at 80 psi. that's over hull speed and just making a bigger bow wave. That engine would be just about the right for the size tug you're doing. Tiny Power suggests that engine for hulls 23-30 feet with a 24" prop. They can get you a proper size boiler too.

-Ron

[fredrosse]

With a tug design you may want to consider a top fired boiler, which can allow the engine room crew or the boat's pilot to fire the boiler while underway. The top fired VFT boiler could be made by anyone who produces conventional VFT boilers. If you look in the "Designing a new engine for a big(ger) boat..." thread you can have a look at how that boiler can fit into your tug, although the drawings presented are for a 35 foot boat, with a boiler more than twice as large (heating surface) as you would require. The arrangement would be very similar for the 27 foot tug.

Has your proposed tug design been built, and if so, are there any available test data from the designer's records? That information would be very valuable in understanding the actual propulsion performance of the hull design.

Fred

[georgepatten]

Well Ive decided to shelve the plans for the 27' tug and go with the identical design but 32' Only 4 1/2 ' feet of headroom in the 27' tug engine room and 6' feet in the 32. I'm 6' and I didn't want raise the cabin roof because of looks, oh well. I've been in the wood boat building business for over 38 years so that part is not a problem. But I need and want to learn about steam engines and boilers and there operation, hopefully not more than my old brain can handle. Looked for the thread that Fred mentioned but could not find it at this time, will look some more.
The larger tug displaces 18000 lbs so I guess I' going to start all over again with regards to power.
George

[fredrosse]

The posts you are looking for are in "Technical - Engines and Boilers", and the subject is "Designing a new engine for a big(ger) boat..." . Presently this thread is about 14 subjects removed from the top of the list, and was started by "Barts". Your design is getting very close to his future plans for a steamer, perhaps the two of you could work something out. Bart has a long experience with steam marine power.

[DetroiTug]

Increasing to 32 feet to maintain the proportions of a cabin roof as drawn is a huge price to pay, the costs and operational complexities are going to increase exponentially. Many of these plans houses are drawing small "periodish" tugs with low to the sheer cabin roofs. They look great on paper but would be impractical if built. And further, they never existed from the period. Tugboats are workboats and the form followed the function. Researching period small tugs for many years now, nearly all of them had ample head room in their houses.

Here are a few examples:









Don't wind up like this guy



-Ron