Posted: Wed Feb 29, 2012 12:05am

Hello I'm in the process of designing a canal boat (bit new to this!). I read somewhere that 2 engines could give you better handling than only 1. I'm considering then using 2 smaller engines (example 2 x 30 hp) rather than a single of say 60 hp. Would this remove the need for a bow thruster? (which I gather is not obligatory, but desirable) Regards

Posted: Wed Feb 29, 2012 8:13am

OK, you say "canal boat". Exactly what do you mean because all "go anywhere" canal boats (called narrowboats) are only 7ft wide or less and for even a full length (72ft) 60BHP is overkill. I am perfectly happy with 36BHP on 54ft. As you say that you are designing your boat I must assume that you are fully aware of the paperwork, demands and calculations required by the Recreational Craft Directive. I must further assume, if you have got to the stage of thinking about engines , that you are fully conversant with the typical underwater shapes of "canal boats" and how that will impinge upon trying to fit two engines. As my own bow-thruster is about 12ft long and sits on the cabin roof, as per the working boats, I could not even say one was desirable. I suggest that you drop this self design idea now it is morning and get out looking at boats that are for sale. Also buy a few magazines, join internet forums (canalworld.net), see if your library has, or can get, any books on canal boat building plus all the ISO standards you should really design and build to. Then talk to the RYA about RCD compliance and CE marking. Then in perhaps three months time when you have clarified what is sensibly possible and what you need to do by all means come back and ask again. Tony Brooks

Posted: Thu Mar 01, 2012 6:12am

Tony Thank you for your advice, ..... however it didn't actually directly answer the question ..... though from your comments you evidently thought it was a bad idea. Fair enough. Though if you don't mind, the choice of whether to design a boat or buy an existing one is really my choice to make. Perhaps it's just something I feel like doing. I don't doubt that you have probably come across all sorts of irresponsible (and sometimes outright dangerous practices), .... however I assure you I have now intention of indulging in such. No, I don't plan to 'design a canal boat' over the week end or something Regards

Posted: Thu Mar 01, 2012 10:10am

The reason I did not answer it directly is because you have not given me sufficient detail. You have only said "canal boat" which would normally imply a narrowboat and then go on to talk about a 60bhp engine which to my mind would imply a wide beam boat. These two things contradict each other and as you make no mention of length I have no way of estimating the turning moments derived for offset twin engines and the wind against boat length. You also do not seem to have taken the typical under water shape of "canal boat" hulls into account - to be honest you come across as having done very little research into the subject. If it is physically possible to fit a pair of engines side by side in a narrow boat (which I doubt) you then have to work out how to design the rear swim area the allow the fitment of two shafts. The most practical way I can see would involve a longish length of exposed shaft and a P bracket. This would tend to reduce the usable length of the boat and I fear lead to an increase in incidents of prop fouling. Even if you managed to fit twin props on a 7ft beam the question then is how large a turning moment they would produce against any wind acting against the hull. With the props no more than perhaps 2.5 feet apart I suspect it would be very little and not worth the effort. If you are talking about a wide beam "canal boat" then the turning moment would be useful, especially as you can get more accommodation into a shorter length (less windage). However that type of boat is still a swimmed design underwater so you are still faced with how to fit twin shafts. Given sufficient skill and/or funds you may achieve this with making a twin swim catamaran type of stern end with conventional stern gear, otherwise you are back to exposed shafts and P brackets. Once you deviate from standard hull forms you are faced with producing scantlings that satisfy the RCD requirements and on the basis of the question I suspect that you would have to employ a naval architect to produce the drawings and calculations. You do not have to comply with the RCD if the boat is built for your own use AND it is not put on the EU market within 5 years of completion. Now, in the present climate I think it would be foolish to assume that you will be able to own a boat for 5 years so building to the RCD is advisable. Then we come to your assertion that a bowthruster is "desirable". This is very much a personal preference and much depends upon the length of your boat, depth of your pockets and how you will crew the boat (note - more things you did not mention). No working canal boat ever had a bowthruster. Although hydraulic bowthrusters are available the majority used on canals are electrical and these present ongoing maintenance and battery issues of their own. Have you researched and thought about the issues? Do you know what a spring is and its use in manoeuvring a boat. That is what the old boatmen used to kick their bow away from the bank or to bring the boat alongside in confined spaces. Have you considered the impact on resale values of a "novel" design? Do you think it is likely that an individual is going to better a design that has had perhaps 100 years of development? Canal Boats are built the way they are for a reason and although not perfect they are by and large fitted for the environment in which they operate. I still question the need for a 60bhp engine for inland use on a narrowboat but would observe that using a single engine driving a hydraulic drive system would allow a hydraulic bow thruster and twin props that may allow the props to be placed further apart the twin engines. It would also allow one prop to be run in ahead and the other is astern. It would not obviate the need to a redesign of the back end and I would not be too keen on the fuel consumption overhead such a system implies. Tony Brooks

Posted: Thu Mar 01, 2012 10:13am

PS - Twin props also imply twin rudders and thus probably twin skegs, further complications to think about. TB

Posted: Tue Apr 03, 2012 4:50am

Tony Thank you for your extensive answer. Apologies for the delayed response (been doing a lot of reading up). Indeed, as you suggest using 2 engines would be quite a headache. As for my reasoning, ..... yes I'm quite new to this, .... so before I go and spend several tens of thousands and 6 months of my life, ... then I should explore all the options, even some slightly unconventional ones. I wouldn't want to get it all done, then find out I could have done a, b or c. For the record, I have obtained/reserved a mooring and it's 48' x 12'. So it might take a very long time to find a boat, meeting my fit out requirements, and of that exact size. It will be a live aboard, so naturally I want to maximise space. I'm trying to reduce the size of the engine compartment. Te length of the engine is then a major factor here. Thus the idea of maybe using 2 smaller (and shorter) engines to be able to squeeze down the length of the engine compartment (and thus increase the size of the cabin) I most certainly intend to get everything done 'by the book' so to speak and implement best practice throughout. I did consider it (the 2 engines option) to be a bit of a long shot, ... but sometimes these things are worth a quick look around to see if it's possible! I must admit I was only hoping for a quick something along the lines of 'well that's not really of any use' or maybe 'yes there are a couple of examples here and here' I perhaps was not aware of your sense of thoroughness (for which I thank you good sir!). As for the design, I do have a background in architectural design/construction (buildings not boats, and have done a fair amount of CAD, liaising with M&E engineers, fabricators and so on. Plus, if I'm going to be living on it for some time, I much prefer to know how it's all been put together and what equipment/systems are used. Well, thank you again for your comments, .... I'll post my slightly unconventional design/proposal for a bow thuster in another topic! Regards

Posted: Tue Apr 03, 2012 7:24am

Now you tell us that you are talking about a wide beam boat then the twin option thing becomes far more possible. However how much cabin space you will gain is open to question because unless you went for a slipper type swim and shallow rounded transom stern the swim shape may force the engines further forward than a single engine would be. However another way of maximising cabin space is to twist the engine through 90 degrees so it is across the boat and use a hydraulic drive system. You will pay a small consumption penalty. With hydraulics you could even put it under the front of the boat. It will also make a hydraulic bowthruster more realistic. Tony Brooks