Oars and engines
If the wind falls calm during a dinghy race there will be rescue boats and probably a committee boat to tow the fleet home. If you are making a coastal cruising passage in a dinghy you should be self sufficient and able to continue somehow. Many dinghy cruisers carry a small outboard motor for this eventuality, others are sailing purists and prefer the simplicity and 'greeness' of keeping to sails and human power only. I do have an engine for my boat but these days I rarely take it on a cruise and I do get a certain satisfaction from managing without it. After all, if you continue with this engine idea a bit further you don't really need a sailing dinghy, you could have a speedboat, or just go by car. Come to think of it why do that, you could just stay at home and look at a web site about sailing. Generally we seem to get pleasure by achieving things and there usually needs to be some slightly arbitrary set of rules to make that achievement difficult enough to be satisfying. Apart the philosophy, an engine and fuel are clumsy items to stow and with most if not all engines there will be some smelly and messy oil and petrol leakage. Having said that, there have been a few trips for which I found an engine most useful, although not essential. For example, in the summer of '98 we sailed to Kent then up the River Medway into the upper reaches where you really could not do much sailing because there are so many bridges and the trees shield the wind. We could have used oars but we would not have got so far in the limited time available.
If you do decide to have an engine then I would advise against buying an unnecessarily large one. Reading the writings of Wayfarer sailors it would seem that a 2 to 3HP engine is enough for a Wayfarer, anything much more powerful will take up more space and use more fuel but give only a marginal increase in speed since speed under power tends to be limited by hull form. I would be wary of an engine salesman who suggests that you should get a bigger engine in case of bad weather or in case you have to tow someone off a mud bank. An engine on a sailing dinghy is not for bad weather, it is for calms and situations where you cannot sail, e.g. because of low bridges. It is not often that you will need to pull someone off a mud bank but if you do then in most cases the best way is to lay out a heavy anchor, either your anchor or the anchor from the boat that is stuck. You don't even need an engine at all this way.
Standards for new outboard motors in the USA require a 75 percent reduction in hydrocarbon emissions from 1996 levels by the year 2006. These standards are not retrospectively applicable to existing motors. Manufacturers are now marketing four stroke outboard motors to meet these low emission standards. Manufacturers are also working on the development of direct injection two stroke engines to achieve low emissions with lighter weight than typical four strokes, but this approach may be mainly applicable to larger engines than are required for dinghy propulsion. If buying a new outboard I would suggest giving consideration to four stroke engines which appart from low emisions use less petrol than conventional two strokes for the same power and avoid the complication of needing oil as well as petrol to run.
When I do carry an outboard motor on my boat I much prefer it not to be on the transom when not in use. With the motor tucked away in a locker the boat looks much more like a sailing boat! Apart from that, the motor is kept dry so that it has a better chance of working when needed, the weight distribution is probably better and the motor cannot get caught up in the mainsheet or other ropes. I know cases of sailing dinghies capsizing because this happened. When arranging a stowage for an outboard motor you do need to take account of any restictions the outboard manufacturer may place on the position of the motor when stored, for example some of them cannot be stored lying on their side. This probably applies more to 4 stroke than 2 stroke motors.
If you don't have an engine then you need oars. Even if you do have an engine you will probably find oars worth having as well. You might break down or run out of fuel and also oars are probably better if you need to manoeuvre your boat in really tight spaces in a harbour or marina. Many racing dinghies carry paddles rather than oars but oars are much better, especially if you are single handed. Using a paddle single handed on a typically beamy sailing dinghy will send you round in circles. With two persons and two paddles it is just about possible but rowing is better for any distance. If as a last resort you have to use a paddle single handed in a sailing dinghy you may do best to sit astride the bows and skull the boat along by working the paddle in a figure of eight motion. This can be useful if you need to move your boat a few yards after you have put up your overnight tent (you can do it with an oar as well as a paddle), but it is not a way to cover any distance.
Rowlocks are quite easy to fit to most dinghies, if not already supplied. There are special (plastic) rowlocks you can use if you need to fit the rowlocks into a buoyancy tank built into the side of a boat. I managed for many years with these but as with most plastic rowlocks they spring apart and release the oar at the most embarrassing moments. Recently I brought some galvanised iron rowlocks and fitted them into turned plastic sleeves which fit plastic sockets in the side decks. These metal rowlocks feel much more solid to row with than plastic ones.
Both metal and plastic rowlocks will sink if they are dropped overboard so it is a good idea to keep them permanently tied to some adjacent part of the boat. If this is not convenient then you should definitely take a spare rowlock or two.
Oars on sailing dinghies are very often shorter than the best length for rowing. The optimum oar length is a function of the width between the rowlocks and the resistance of the boat to motion, a light easily driven boat can utilise slightly longer oars then a heavy one. There are various formulae for calculating oar length on the internet but for most sailing dinghies it is best to get the longest oars which you can stow in the boat, the chances are that they will still be too short. If you should be designing a boat for dinghy cruising then oar stowage is something to think about from the beginning. On my purpose designed boat I have stowage for the oars each side of the cockpit and above the level of the rowing thwart. That way the oars can be used quickly without having to get them out of the bottom of the boat where they are under the thwart and possibly buried under baggage.
If you would like to make your own oars then a simple and effective method is to glue plywood blades onto a shaft rather than building up the whole oar from solid timber as the traditional method. For most sizes of dinghy the shaft should start at about 50mm x 50mm section and is then planed octagonal before rounding off all the corners, a satisfying job and if you use an electric plane it will be done in no time. If you are going to use the plywood blade idea then the outer end of the oar can blend from a circular to elliptical section which then becomes a D section so that the blade can be glued to the straight side of the D. If you make this face curved you can form a blade with a slight spoon shape. 6mm ply is quite thick enough for the blade. Sitka spruce is one of the best woods for making oars, albeit expensive. Sitka spruce is one of the lightest woods and was used for racing oars prior to the advent of carbon fibre. For general purpose oars some people recommend harder woods than sitka spruce, eg ash or pine since these are less easily bruised by being knocked about.
I remember a tip from Eric Coleman for applying fibreglass to the ends of oars to protect them when they are used as punting poles, which tends to happen with oars on cruising dinghies. You wrap a few layers of fibreglass tape or cloth impregnated with resin (epoxy is best) round the end of the blade and positioned so that it overhangs the end of the blade by perhaps 6 to 10 mm or so. This forms a little pocket extending beyond the wood of the blade. After the fibreglass has hardened you can then stand the oar on end so that this pocket can be filled with a mixture of resin and scraps of fibreglass off cuts or a suitable proprietary high density filler. When that has hardened you will probably have a horrible looking mess with spikes of fibreglass sticking out everywhere. However, a few minutes work with an angle grinder and coarse disc will shape this so that you end up with a solid fibreglass blade tip extending beyond the end of the wood and that should last for years of shoving off mud banks.