High Speed Narrowboat

[Nick Ireland]

Does anyone have information on a suitable design for a high speed boat with low wash suitable for carrying passengers on a canal? Maximum dimensions would be 6ft 10" wide by 70ft long.

[SailDesign]

Nick - define "high speed". Comapred to _other_ narrowboats or do you want to plane?
Are there not actual speed limits on most of the canals, regardless of wash created?
Steve

[badges65]

Hi Nick,
thats a very long boat for its beam!!!
a variation of the IVB will give you a hull with no BOW WAVE and reduced wash, I would be looking a a version similar to willinghoff's version but with our chine version .
don

[CDBarry]

You need to look into the issue of critical and super critical speed.

Wave celerity is a function of water depth and both resistance and generated wash are very sensitive to the hydraulics of the canal itself. There is a magic speed that is very easy to acheive, a sort of "sound barrier" which is hard to overcome and then another regime of speed which is easier.

This is a very high tech topic that is the subject of significant work in hydrodynamics texts, and more recently some fast craft symposia (Fast '99, Fast 2001, etc.) and you should research it carefully.

[Nick Ireland]

Many thanks for your responses. There is a speed limit on the canals of 4mph. We are exploring the idea of a specially licenced boat which would be capable of 10-12 mph. It would run on a relatively straight section of canal and might be restricted to certain times. Horse drawn passenger boats (called fly-boats) ran in the 19th century reportedly at an average of 10mph.

The dimensions of the boat are the limits of what can go through a lock. There are routes that a wider boat could undertake.

In fact it is exactly these fly-boats that led Froude to formulatng the mathematics that gave an understanding of the hydrodynamics of waves, both in general, and in channels, in the 1800s.

They operated at the critical speed for the canal, and since it is bounded on both sides, wave energy could not be radiated away and they travelled with the wave they generated with little losses and very low drag. They essentially surfed on their own wave.

They do, however, produce a very substantial wave.

From a viewpoint of channel erosion, you have to examine the components of the wave. It is mainly transverse flow that causes erosion.

Again there is currently a good bit of research in this matter. Since you are in the UK, it would probably be worth going to the RINA library in London and generally contacting them for recommendations as to experts in this area. It is a few blocks from Victoria station.

[Peter_T]

A long but narrow boat configuration resembles to the canal canoes or the dragon boats. But beware that the beam reduction must not be approached to the critical slim form as to hinder stabiltiy. The first approach is to ensure that, there is adequate stabilty so that all persons onboard with gear can stand up on the deck. In the case of the racing canoes, some requires that the operators to be in the sit down position. The next step is to check on freeboard to ensure that the boats can roll over a certain angle with good residual stability. In simple terms, the boat must be able to handle dynamic roll, that doubles that of the static heel caused by wind, steering or offseting passenger. Also account for dynamic stability to resist rolling angles caused by the passing boats or rolling in the unresisted ambient wave condiions. Moderately increasing the beam and depth will solve these problems.

Your quoted inland navigation speed was so low about 5 mph i.e. like 4 knots. Most cities will limit to about 8 to 10 knots. Wave wash is a critical matter. In Germany wave wash effects and craft design restrictions are under review and some serious research efforts have been made. Their speed limit is in the higher speed range and they are investigating high speed craft limits.

At this point, it is hard to proposed on a suitable hull form, without knowing what is the canal sectional dimensions: e.g. mean width, mean depth or critical depth. You see the canal effect on a craft may be closely related to model testing in a basin. A large model tested in a small basin will have shallow water effect, generating deep and short waves. Powering boats in shallow waters, spend more energy to run at the desired speed compared with the condition in deep water region, before entering the canal.

Canals are usually depth restricted, so only multi-displacement hulls will run properly in comparison with the mono hull. A flat bottom boat will restrict the water flow near the river bed, thus creating shallow water waves and vibration.

If you look at the market of pleasure boats, there is a trend of twin pontoon platform boats. These boats will best suit the operation in the wave wash ban area. However, these boats are usually in round pontoon with conical bow, but are economically blunt ended. They also lack reserve buoyancy one the water wash over the top of the pontoon. If you get both ends of the pontoons in faired ended so that the bow breaks in the water set up some wave, the stream can flow smoothy to the stern with setting another train of large divergent wave due to blunt stern end.

The simple trick in breaking the wave size is to reduce the beam and provide a small angle of entrance and ensure good stern streamline shape. The modern idea is to subdivide the hull to two or three parts, the wave effects will be lessen, even after adding up the effects from the number of pontoons involved in supporting floatation. Increasing length is a prime improvement in lowering the wave effect.

From the web, there is a 4 mph limit:
http://www.murray-river.net/boating/pwc/default.htm

This limit protect the envirnoment, but limit in boat construction.

Now look at another fast ferry speed limit:
http://www.marlborough.govt.nz/harbo...rries_main.asp

Peter

[philwhittaker]

There ia an outfit in san diego that has patented a design called the M hull. It is used in cannals in venice for passanger craft and is designed specificly to reduce the wake while keeping the passanger volume.

[Peter_T]

Thanks for leading to the M hull. An impressive hull form using two tunnels, carried all the way aft. So it is in fact a trimaran, except that there is no air gap to enable her to ride in rough waters. Unless, it is using activated air cushion.

http://www.aeromarineresearch.com/history.html

I don't suppose the Venice authority will allow them to run at automobile speed along side the traditional Gondolas. A low speed, much more power will be needed due nearly doubling the wetted surface.

The canal is approximately 10m wide and 1.2m or more deep. It is brick lined both sides on the main route we are looking at. Generally the channel is deeper in the middle and may be shallower at the edges.

Is a multi-hull design feasible for a 7ft wide boat of this length? Passenger space may also be an issue. A traditional narrowboat has very little spare headroom and greater height on the boat would restrict areas of use.

Many thanks for all your comments

Nick

[Peter_T]

For such a shallow chanel of 1.2 m or 4 ft, it will be necessary to limit the boat draft to 0.6m or 2 ft. Shallow water effect will come in. To copy the Venice situation, one can make a catamaran with two gondolas. Their streamline hull is ideal for the channel transit, with the least wave wash effect.

A similar situation is in the polynesian culture village HI, there are lots of catamaran boats for supporting folk dance shows and for visiting folks. They are great platforms and can be outfitted with outboard motors.

Peter

[SailDesign]

If memory serves me, the maximum "air draft" on a canal is about 2m. This would mean that when the boat is _empty_, it can only be 2m tall, and obviously water draft is limited when the boat is full. That would, as the OP says, leave little headroom. In a multihull as Peter_T describes, it would not even leave much more than sitting headroom.
Steve