LOCATION OF ENGINE CONTROLS

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PeterDiana
Inlägg: 3
Blev medlem: sön 19 aug 2007 14:39
Ort: otterbourne

LOCATION OF ENGINE CONTROLS

Inlägg av PeterDiana »

We are considering purchasing an IF without inboard. We intend initially to use the boat for coastal cruising and in the very busy waters of the Solent in UK, with several crowded marinas. In places, tidal currents here also reach 4 to 5 knots. There are times when powerful engine drive and easy/quick starting are needed. We are used to bigger boats (10 to 12 metres) with inboard diesel engines.

We are considering installing a long shaft 8hp four stroke Tohatsu (max revs 5000rpm) with remote engine controls, battery charging and electric start. Does anyone have any ideas about where to fit the control box (gear and throttle levers). We would also be grateful for any other views gained from experience - for example, will the lazarette lid have to remain open during engine running?

Later we shall be sailing in less crowded waters and will put a small outboard in so that we can race within UK class rules. We shall then remove the control box.

Thank you very much to anyone who can help.

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maja
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Inlägg: 2341
Blev medlem: lör 19 aug 2006 08:56
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Inlägg av maja »

It is a common misunderstanding that it is possible to overtake current with a stonger engine. Current does not generate any forces on the boat except from some small relative vind speed force, i.e. for example a current of 5 knots will generate a relative wind speed component of 5 knots in the opposite direction.

So if your engine already generates max or near max displacement speed through water (about 5.5 - 6 knots for an IF-boat), you will not gain any remarklebly better performace against current with a stronger engine.

But with a stronger engine, low max RPM type (max RPM is to be approx. 4500 or lower), and with a propeller with low pitch your performance will be better in moderate or strong wind ahead conditions and in a heading sea.

Additionally, it is not very likely for a large modern 8 hp 4-stroke to fit in the motor well in the lazarette. The motor will probably be too large. You have to check this carefully, also that it will be possible to close the hatch whe the motor is fitted.
Marek, IF-båt SWE-829 "Ingela" från Lagunen i Malmö
Medlem i IF-båtförbundet sedan 1985
IF-båtägare sedan 1983

PeterDiana
Inlägg: 3
Blev medlem: sön 19 aug 2007 14:39
Ort: otterbourne

LOCATION OF ENGINE CONTROLS

Inlägg av PeterDiana »

Thank you for these thoughts. I am a qualified engineer so I understand your points clearly.

The conditions we have here quite often in the afternoon are: a wind of force 5 / 6 (above 20 knots); plus a tide of 4 to 5 knots through the narrow gap between the Isle of Wight and the mainland coast; and shallow but variable depths (1 to 60 metres, mostly about 20 to 30 metres in the middle of the channel). I do not believe that a 4hp engine will allow the boat to achieve hull design speed (5 to 6 knots) in these conditions and so the boat will probably go backwards.

Also, you may already know that our marinas have very narrow channels and tight turns compared with the marinas on the Swedish West coast and the Norwegian coast up to Oslo. They are also very crowded: often the boats 'raft up' side by side with two or three on one pontoon space. Also, there is much commercial shipping in the crowded channel going in to Southampton - hovercraft, fast catamaran ferries, container ships and cruise liners and oil supertankers. So we must be able to manouevre under power when necessary (I was taught to sail without engines, and have sailed that way in the Kiel Bight and Lille Baelt), and the engine must be capable of accelerating or stopping the boat quite quickly (i.e. it must be 'responsive').

I think you are right that we may have to leave the locker lid open.

I believe from your previous messages that you use a Yamaha F4 long shaft: what length is it? We have the option of 20 inches (510mm) long shaft, or 25 inches (635mm) extra long shaft.

Thank you again

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maja
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Inlägg: 2341
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Inlägg av maja »

I am an engineer as well (MSc) and have handled different matters of ship technology during all the 35 years of my professional period. Presently I am working with submarine applications.

My Yamaha F4 shaft is 20 inches. I do not think there exists longer shaft for that type of engine.

For 20 knots of wind ahead such a motor will perform not more than 4 knots through water and more likely about 3-3.5 knots. Anyhow, a motor mounted on the transom as mine will thus be uselesss, as there will be waves and the propeller will be in the air most of the time. So I use the sails whenever possible. It is faster, better and safer to use the sails in windy and wavy conditions.

For a tide current of 5 knots ahead or more my opinion is that it will be dangerous and obvoiously not very possible to make any considerable distance with a boat of displacement speed of only 5.5 - 6 knots. It is wiser to remain in harbour or anchored.

If you insist, I recommend you to buy a boat with a strong and reliable inboard diesel engine (About 15 HP for an IF) and equipped with a 2 fixed blades propeller with a pitch (very small) well tuned to the RPM of the "economic" speed of the engine.
Marek, IF-båt SWE-829 "Ingela" från Lagunen i Malmö
Medlem i IF-båtförbundet sedan 1985
IF-båtägare sedan 1983

PeterDiana
Inlägg: 3
Blev medlem: sön 19 aug 2007 14:39
Ort: otterbourne

LOCATION OF ENGINE CONTROLS

Inlägg av PeterDiana »

Thank you for your long and detailed responses. Your experience and advice are very useful and helpful for us. We shall continue to think of options.

euanb
Inlägg: 11
Blev medlem: tis 30 jan 2007 11:21
Ort: Mylor, Cornwall, UK

Inlägg av euanb »

You might be okay with an inboard boat.... your handicap will refelct the choice on engine and prop. Down here in Cornwall, most of the boats have outboards but the three inboard boats racing have an allowance that reflects the type of prop. 1% allowance for a two bladed feathering, 2% for a two blader fixed and 4% for a three blader fixed. I believe this is a standard RYA allowance on any keel boat of the same class. I have only raced in two regattas so far as I got the boat this summer, but it would seem a fair system.... we struggle most in light airs reaching with the fixed three blader, but will change to a feathering prop over the winter.

Are you planning on moving the boat down to Cornwall?

Suzanne
Inlägg: 28
Blev medlem: fre 23 mar 2007 14:19
Ort: Boat in Oslo fjord:Sande

Inlägg av Suzanne »

I have a remotely controlled outboard, however without electrical start, so that procedure still requires visits to the aft deck.

The control box is mounted onto the vertical wall on the starbord side of the footwell, quite far aft. Well within reach for the helmswo/man, still out of the way.

Please bear with my clumsy terms. :oops:

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