Has my Dolphin lost a "flipper" ??????

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MasterofHera

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Has my Dolphin lost a \"flipper\" ??????

Dolphin petrol engines may not be everyones cup of tea but mine starts and stops and goes astern with no problems. This is a new installation in my FB (its old but ran well on the bench ). Slow speed manoeuvering is fine BUT when I ask for power I get little or no responce .....the engine seems "flat".
During instalation one of the 2 coils was damaged and oil has leaked from it .....Is it an electrical problem?
The cut out in the rudder is for a different prop ...could the size of the cut out be of significance?
With the engine stopped the shaft turns freely in the bearing. I disconected the shaft (2nuts) shaft turns freely . With shaft disconected engine revs normally as on the bench.

I have run the engine tied up to the pontoon this engine set up will not "rev" under load. Help please.
Mike.
 
Re: Has my Dolphin lost a \"flipper\" ??????

Hi sarabande
thanks for your interest and input. I cannot tell you the distance between deadwood and prop. The rudder will have to come off anyway as the prop foules the rudder on full lock. My fault should have tested it before going back into the water but it looked alright at the time! There was room to fit a rope cutter on the shaft. Its a small high speed prop ,could the rope cutter be obstructing the flow of water?
 
Re: Has my Dolphin lost a \"flipper\" ??????

propellor clearance from the nearest part of the hull is quoted variously as being at least 10% to 15% of the diameter of the prop.

Clearly, if the rudder is fouling the prop, it is too close and may therefore be impeding the flow onto or away from the prop.

What happened to the previous prop ? How do its dimensions / pitch / number of blades compare with the present one ?
 
Re: Has my Dolphin lost a \"flipper\" ??????

"I an led to believe" that previous engine was a BMW deisel. The boat came with no engine but the shaft and prop were in place. Prop was 2 bladed and was larger than the Dolphin prop luckily the shaft diameters were compatible. The Dolphin came complete with all electrics and shaft and prop having been removed from a FB. The removal was a subject of an article in PBO about 5yrs ago.
 
Re: Has my Dolphin lost a \"flipper\" ??????

Just a thought .....if the prop was in the shadow and not receiving sufficient flow of water across it, wouldn/t the engine rev more freely?
 
Re: Has my Dolphin lost a \"flipper\" ??????

When power is applied their is a natural tendancy for the shaft to move forwards or back depending on if you are in ahead or astern. (unless you have an Aqua drive type arrangement). Could this be causing the rope cutter or prop to foul on the rudder or cutlass bearing?

When you say oil leaked out of a coil was it an HT coil or one of the 2 multiple contact coils that enable ahead/astern and starting? Only other thing to check is the jets on the carb. A good hard blow through to ensure both pilot and main are clear will ensure adequate fuel is getting through. Water can also do this but is more likely at idle than when at power.

Yoda
Now A dolphin Mk2 owner!
 
Re: Has my Dolphin lost a \"flipper\" ??????

the flow across the blades is a complex fluid mechanics issue, and there are sites which will give lots of details, e.g.

http://www.olds.com.au/marine/propeller_faq.html

http://www.hydrocompinc.com/knowledge/techexchange.htm

AFIR if a blade is close to the deadwood as it rotates, it is hitting almost stationery (non-flowing) water, and there will be a stalling effect, and probably lots of extra vibration. So proximity could in fact slow the shaft down, especially on a relatively small engine. Propellors like working in moving water, as it reduces the slip % and makes them more efficient. There are all sorts of developments in cupped and shafted (tunnel) props, which are much better than trad screws.


Also, it is frequently forgotten that shallow water will increase drag especially for a single prop boat, because the propellor "feels " the water in a different way from in deep water.

It's not like a centrifugal pump which speeds up if the inlet is blocked.
 
Re: Has my Dolphin lost a \"flipper\" ??????

Sounds like your engine is lacking power. All the posts about prop etc. are fine except that an engine will often cavitate on full throttle when tied up - this allows the revs to go up near full.
Even if it does not cavitate, if you have correct prop. the engine should rev.

So as I suggest, it sounds like you may have low speed fuel power, but when opening up and demand for high power fuel delivery it's not there.
Not same engine, but similar happened with a previous boat we had and the Vire fuel system failed to deliver main jet supply. Idle jet was fine and engine started easily. Out of gear it would rev freely.
The prop clearance to rudder obviously has to be sorted, but doubt taking your description that it's the reason.
 
Re: Has my Dolphin lost a \"flipper\" ??????

Thanks everyone ..........we will get in the water tomorrow take the rudder off and have a look at it. SWMBO has her own wet suit .....!!!!!
 
Re: Has my Dolphin lost a \"flipper\" ??????

Thanks everyone
This Dolphin engine came complete with electric fuel pumps and a Filter King but at this point I have not made use of them. I have used a gravity fed system which appears to run the engine at low revs but under load does not produce power Have I got it wrong?
 
Re: Has my Dolphin lost a \"flipper\" ??????

Lacks power? two stroke? If it was a lack of fuel they tend to splutter and die - I would check the exhaust system and the exhaust port for heavy coking. This is a classic problem with old motor bikes.
 
Re: Has my Dolphin lost a \"flipper\" ??????

[ QUOTE ]

Lacks power? two stroke? If it was a lack of fuel they tend to splutter and die - I would check the exhaust system and the exhaust port for heavy coking. This is a classic problem with old motor bikes.

[/ QUOTE ]

Typical 2 st problem is crankcase seals deteriorated and then engine cannot draw proper fuel amount, but in it's early stages engine will often run free and appear Ok until load comes on.
The other more common is where idle jet in carb is ok and engine starts and runs, but main jet is restricted - again all seems fine until load comes on and again engine does not rev.

Splutter and die is often when the crankcase seals are near finished.

Judging by the original post - I still consider carb jets as restricted, or engine is not being fed sufficient fuel for load use.
 
Re: Has my Dolphin lost a \"flipper\" ??????

Hi yoda
The coil was No.2 HT. Will check the carb for blockage. I dont think the rope cutter is touching the cutlass bearing but will check today when we remove the rudder.
 
Re: Has my Dolphin lost a \"flipper\" ??????

Many thanks everyone.
Removed the rudder today and reshaped it to avoid the prop. It came off easily but I suspect replacement will be a bit of "wet" fun. Ran engine with rudder removed no difference in engine performance. Deceided to take the electrics apart.Put a strobe in line with plugs and leads (new ones) under load No.2 spark trails off. Suspect the damaged coil. Changed leads over incase it was the lead ,no diference it must be the suspect coil. Luckily it has separate ignition for each cylinder. Removed contact breaker cover ..both contacts "sparking" . Well tomorrows another day so will swop coils!!!!!!
 
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