The Steamboating Forum

Two aluminum angles, 2 inch x 2 inch x 1/8 inch are bolted through the hull to act as bilge keels, about 2 feet apart, about 6 feet long each, to keep the boat tracking properly. Inside the hull, the thru-bolts attach to wood stringers for mounting floor boards.

The stern shaft bearing (1 inch diameter shaft) is a WW Grainger food service UHMW plastic spherical bearing, with a pressed stainless steel mount. This bearing has been in the boat for 14 years, initially with the 3/4HP electric motor, and now with a 13 horsepower 1000 RPM IC engine drive, bearing is still very good. The struts holding the outboard bearing are 1/4 inch x 2 inch steel flat bar, extending out to the bulge keels.

This configuration of angled braces can take considerable side loads, like the ones you get when the turning propeller hits an underwater obstruction.

The electric installation. The 1 inch main propeller shaft is about 6 feet long, and I used a Home Depot PVC sink drain fitting as a stuffing box for the shaft, with some greased twine as packing. Believe it or not,this $2.00 fitting is still in service, all OK!

Electric boat, ready for its first outing.

The boat is almost all e-bay purchases:
Boat with trailer, with broken mast, $107.
I then paid the guy I purchased the boat from to fix the trailer, new tires, new bearings, new lights, and deliver to my house for $250.
Pacific Scientific 3/4 HP 24 volt DC Continuous duty PM Motor, New, $40.
Bronze 3 blade prop, 14 x 16 RH, slightly damaged, but OK at 400 RPM, $35.
Two Group 27 Marine batteries, new @ $69. each (now batteries are far more expensive)
Plus about $100 for jack shaft and bearings, pulleys, cables, etc.

The Javelin looks like a nice dinghy for steam conversion. At 14 feet long it would make a nifty "pocket" steamer.
The fiberglass seats provide built-in flotation, a good safety feature. Hulls were constructed until the end of the 1980s.

The Thistle design came from the smaller International 14 sailboat. Not a one-design boat like the Thistle, but still with that nice vertical bow.
Water line length = overall length.
An English class design, they allow unlimited sail sizes and are all-out racing machines. I have seen some insane setups.
Hulls have been built of all materials. More food for thought.
RussN

Cheers Fred, those sizes work well, I was hoping to get away with something much shorter, but I'm not sure yet, I haven't put any final thoughts Pete's way yet, or drawn them.

Hi Folks

Thanks for all your posts.

I have just stumbled across a nice photo of the Stornoway 12 which shows what a pretty boat it is but does emphasise just how small a 12 boat is.

The boat in the photo is for sale. See: [https://www.davidmorrisboats.co.uk/blo ... nghy-1900]

Pete

Hi Everybody

Here in Wales the Welsh Government has lifted most of the Covid 19 restrictions, but it looks as if nobody told the Weather Department. It is cold (10.9 degrees C), windy and wet which made it seem ideal for yet another session in the Office with the computer. However, this time I have come with my shiny new copy of Dave Gerr's Propeller Handbook that I have read once and am now struggling to use. https://brownsbfs.co.uk/Product/Gerr-Da ... 0071381765 (11.19 GBP for the original edition or 18.99GBP for the Second Edition).

I have also been working on the drawings and, following the discovery of Simpson's Rule, can offer you some data with which to play:

Displacement = 19.14 Cu Ft, 571 lbs or 259 kg. Typical build weight is 45 kg.
LCB is zero.
The Block Coefficient is 0.00000052 (Slippery as an eel!)
Waterline length 3680mm, 12.07349 ft.
Breadth is 980mm, 3.21522 ft.
Draft 139mm, 5.47244 inches.
V = 4.66 knots, 5.36 MPH.
Power requirement by rule of thumb is 0.45hp.

The output I have generated using Dave Gerr's book is as follows. Some items do not seem to be quite right to me. Part of the problem is that for such a small light boat the calcs are all off the bottom of his charts.

Power requirement (SHP) = 0.47 HP
SL = 0.088

Estimated Slip = 0.583%
Suggested propeller size - this varies significantly with engine revs:

Summary Table
Shaft Speed---Diameter “ ------ Pitch “ Pitch Ratio
300 ---------------- 13 -------------- 19 ------- 1.46
350 ---------------- 12 -------------- 16 ------- 1.33
400 ---------------- 11 -------------- 14 ------- 1.27
450 ---------------- 10 -------------- 13 ------- 1.30
500 ---------------- 09 -------------- 11 ------- 1.22
550 ---------------- 09 -------------- 10 ------- 1.11
600 ---------------- 08 -------------- 09 ------- 1.13

The original hull design in the sailing mode (i.e. with a keel and skeg) suggests only space for a 6 inch propeller if the propeller is not to drop below the line of the keel. Given that this is the sort of boat for exploring little creeks and shallow waterways it would be a shame to increase its draft with a lot of bronze hung under the stern. Thus I was idly wondering about twin screws. The idea has been well tried by the Victorians in the launches that they built for work in the 'Colonies'. Whether it would be possible today I am uncertain. There are certainly plenty of very small plastic propellers offered on eBay, though I have seen none that are left handed.

Addendum: I have done a few more calcs. I have assumed that the slip figure for a single screw is the same as for a twin although strictly twin should do slightly better. I have also assumed that the shaft horsepower from the single screw calc is split into two for the twin calc since there would only be one engine. The figures that emerge rather suggest that it is hardly worth the bother:

Shaft Speed---Diameter “ ------ Pitch “ Pitch Ratio
300 ---------------- 11 -------------- 19 ------- 1.73
350 ---------------- 10 -------------- 16 ------- 1.60
400 ---------------- 09 -------------- 14 ------- 1.56
450 ---------------- 09 -------------- 13 ------- 1.44
500 ---------------- 09 -------------- 11 ------- 1.38
550 ---------------- 08 -------------- 10 ------- 1.25

Thus it looks as if a shaft speed of 450 would work best with a single 10" prop. Fred was right way back at the start! I will now have to look at the bits in Gerr about more blades and the amount of clearance next.

Regards

Pete