Newboy Posted March 31, 2004 Report Share Posted March 31, 2004 I'm a novice at boat fishing, I'm working my way thru the 18' Shetland I'd bought over the winter. I've fitted a new deck, replaced the cushions and rewired the lights as well as power points. The boat came with honda 10 hp outboard, but I've decided a bigger engine is required for seafaring (it was used in the river only), so a 30hp Johnson was bought. Now, should I keep the honda and use it as an aux engine? The upside is that I know the honda is a good engine, just serviced and the chap said it's in pristine condition. The downside is that (to my discovery) both engines weigh a considerate amount if both are fitted. With the trailer parked on a slight slope, the combined weight of the engines, and me trying to jump up, it lifted the jocket wheel of the ground. Or should I get a smaller ob like a seagull which can be stored inside the boat untill needed? Plus it weigh a lot less. Also, how small is small (minimum) to push a 18' boat in an emergency? Thanks in advance. P.S Anyone know what this boat is, I know it's a shetland but not sure of model. Quote Link to comment Share on other sites More sharing options...
Adam F Posted March 31, 2004 Report Share Posted March 31, 2004 Hi Newboy, Welcome to the site. Very good question - which raises several points. This is the way I would see the situation. You have an 18' boat , a Shetland (fairly heavy design) so a small aux. say a 4hp, wont really be of much help - even on a 16' dingey they are only good for emergancies, and for aux. propulsion you wont get abpve 2/3 knots max, in slack tide. So to give any really assistance - youll probably need about 10hp - ideal as this is what you have. You mention a seagul. Great aux. engines, although any outboard doesnt like being laid down, and stored flat - so I would advise against this. The 10hp you already have is in great condition and as you know it, should be realiable (this counts for alot with engines) My own boat will raise the jockey wheel if I jump off the back whilst on the trailer, so dont be too alarmed - the real test will be to fit them and see how she sits in the water - swamping over the transom will be you biggest risk. If she sits fine - then in my opinion, whack the trusty 10hp on the back. Cant help with the model - Im afriad, Try a good search of the web. Hope this helps Adam Quote Link to comment Share on other sites More sharing options...
Maverick Martin Posted March 31, 2004 Report Share Posted March 31, 2004 Hi Newboy I agree with what Adam has stated above. Much smaller than 10hp and you wont move to far especially against a tide. A 30hp engine will probably give you around 14/15 knots, maybe less when loaded up. The boat should be able to take up to 50/60hp With regards to the boat it is definatley a shetlandsuntrip Martin Quote Link to comment Share on other sites More sharing options...
Paul D Posted March 31, 2004 Report Share Posted March 31, 2004 Martin, My Orkney 520 ( 17 ft long ) has a 30 HP Honda 4 stroke and manages 17-18 knots loaded up. ( 9 knots when engine in need of service ). I am actually pondering over getting an aux engine. Need to get a bracket first ! Quote Link to comment Share on other sites More sharing options...
Paul J Posted March 31, 2004 Report Share Posted March 31, 2004 I have a Yamaha 5hp so i you do want to consider a trade. I'm your man Paul J Quote Link to comment Share on other sites More sharing options...
Afishionado Posted March 31, 2004 Report Share Posted March 31, 2004 To answer your question I best try and explain a bit about hydronamics, and before you go cross eyed it's all quite straight forward. A boat floating IN the water has a maximum hull speed of 1.5 X the square root of the water line length. So your boat will not exceed 16 x sq root x 1.5 = about 6knts. If however you have enough power (and thrust) to push your boat ON TOP OF THE WATER (planeing) your speed is only limited by the amount of power you can apply (known in the nautical world as 'kin flying). How does this affect you.......... With the 10hp engine you will not reach the speed needed to plane, therefore you will only get to about 6knts. There are a lot of lighter lower powered engines that will give you this performance too. The slower the engine turns the prop, and the bigger the prop is the better. Because what you want to maintain a steady speed is a high VOLUME of water thrust out by the prop. A small high reving small prop is useless. Basicly the best engine to do this is a Seagull 100 (the big one). They are noisy and thirsty but they are bullet proof and reliable. They don't mind being laid down (Just not upside down), however for safetys sake any aux' engine is best permanently mounted on a bracket. You don't want to be trying to hang an outboard on the transom whilst bobbing about on the briney . Brackets and outboards can be found on e-bay. Mike Quote Link to comment Share on other sites More sharing options...
Adam F Posted March 31, 2004 Report Share Posted March 31, 2004 Paul - I have a hardwood engine bracket FOC if you want it. Alu body, and hardwood plate - about 60 quid in the shops. Let me know. Adam Quote Link to comment Share on other sites More sharing options...
Paul D Posted March 31, 2004 Report Share Posted March 31, 2004 Adam, That would be great thanks. Will it be possible to bring to the meeting tomorrow ? and if in really good condition I will tear up your FF cheque ! cheers Paul Quote Link to comment Share on other sites More sharing options...
Adam F Posted March 31, 2004 Report Share Posted March 31, 2004 Good condition? - Never been used! Quote Link to comment Share on other sites More sharing options...
Newboy Posted April 6, 2004 Author Report Share Posted April 6, 2004 .......Basicly the best engine to do this is a Seagull 100 (the big one). They are noisy and thirsty but they are bullet proof and reliable........ Mike When you said the seagull 100, is that same as the seagull century (since it's 100)?! Quote Link to comment Share on other sites More sharing options...
Afishionado Posted April 6, 2004 Report Share Posted April 6, 2004 Dat's der Bunny!! As I said they are relativly bullet proof, and produce enough thrust to push a heavy boat albeit at a slow speed. Mike Quote Link to comment Share on other sites More sharing options...
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