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Jason
Jason, Marine Mechanic
Category: Boat
Satisfied Customers: 15356
Experience:  Degree in Marine Technology. Gas and diesel marine mechanic.
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I have 3.6m inflatable with a Tohatsu M40C outboard. The

Customer Question

Hi, my name is***** have 3.6m inflatable with a Tohatsu M40C outboard. The outboard seems to be low on power i.e. getting up onto the plane takes a while in calm water with only one person in it. Once up on plane it zooms along at 20mph fine. But when the water is choppy forget it - even at WOT the boat makes very slow headway. Cylinder compression is good at 130+. Fuel system seems ok and I've stripped and cleaned fuel pump and carb etc. No gunk in either. Bowl and jets clean. Motor is on a Panther tilt/trim unit. I've played with trim and found what seems to be the best angle. The motor was serviced a few months ago - although fuel pump wasn't touched at that time. Any thoughts?
Submitted: 7 months ago.
Category: Boat
Expert:  Jason replied 7 months ago.

Hi Paul, my name is***** am reviewing your question and will respond momentarily.

Expert:  Jason replied 7 months ago.

Okay I read everything. Is there a history on this engine and boat combination that you can share with me? How long have you owned it for, has it ever been any better or different for you in the past? Or did you just buy it, and this is the way it is?

Customer: replied 7 months ago.
Hi - I've only owned the boat 9 months and it has performed like this since we first put it in the water. I bought the boat second hand.
Expert:  Jason replied 7 months ago.

Do you know what the boat is rated for horsepower wise?

Customer: replied 7 months ago.
Actually there are a couple of other more superficial issues with it at the moment i.e. not starting due to broken solenoid - at least I think that's the issue. It's doing a rapid click when I go to start it - have replaced battery, checked wiring etc. So have ordered a replacement solenoid. Also it is a little difficult to start - and once started it splutters out after 5-10 seconds and has to be restarted. I have to do this 3 or 4 times before it stays going. But aside from these the bigger problem is the lack of power. I would've thought a 40HP engine should push a 3.6 inflatable with one person in it with no problem. That said the engine is a little heavy for the length of boat - and so the stern is lower in the water than it should be. So there is that weight disadvantage to over come when getting out of the hole initially.
Customer: replied 7 months ago.
I think typically the boat is rated for 15 to 30hp. So 40 should be tons.
Expert:  Jason replied 7 months ago.

Do you know if the shaft length of the outboard is correct for the boat? Do you happen to have any pictures you can share with me showing how the outboard is mounted to the boat?

Customer: replied 7 months ago.
To be honest I am not sure. I will have to go and check. I can get some pictures. It will take me 20 minutes or so. Back to you soon.
Expert:  Jason replied 7 months ago.

That will work. Take some pictures from the back of the boat so I can see how the motor is mounted, and how high or low it is in relation to the bottom of the boats bottom.

Customer: replied 7 months ago.
Hi - here are some photos. The boat's in the water so difficult to get the right angles. Also the height from transom top to bottom is about 56cm. And the height of the leg from the top of the cavitation plate to the underside of the motor - where the leg bolts on is also about 56cm. Also the Panther tilt mechanism sits about another 5 to 10 cm above the back of the transom - so that means the prop isn't quite clearing the bottom of the transom ...
Customer: replied 7 months ago.
When I first got the boat it didn't have the panther on it. And I didn't drive it before the panther was put on. So perhaps the panther has changed the dynamics - tipped the balance so to speak. I've played with the tilt on the panther vs motor using the outboard's built-in tilt to see if tilting it down further helps. But it doesn't seem to. The sweet spot is about the middle hole on the motor's tilt bracket and then the panther takes over from there.
Customer: replied 7 months ago.
Note - from photo - year of manufacture was 2002. Recommended outboard power is 25hp (18.6kw). Weight is 63kg.
Customer: replied 7 months ago.
Whoops - the previous note applies to the boat - not the motor. And sorry ignore the weight. That should be 630kg and is the weight of people and luggage.
Customer: replied 7 months ago.
weight of outboard.
Expert:  Jason replied 7 months ago.

What I needed to see what the relationship between the propeller and the bottom of the boat. Are you able to, or do you have any pictures with the boat on a trailer?

Customer: replied 7 months ago.
I have one before the motor was mounted on the panther. i will send it in a minute.
Customer: replied 7 months ago.
Hi - photo attached. Note the hydrofoil blades have been removed currently to see if they made any difference.
Customer: replied 7 months ago.
Form the photo the leg looks long enough - even if the panther raises the motor by 5-10cm - but maybe that makes all the difference ...?
Expert:  Jason replied 7 months ago.

If you look at the fins above the propeller. Are those above, even, or below the keel/bottom of the boat?

Customer: replied 7 months ago.
I've removed the fins. But I will need to go check. Can you wait another 20mins?
Expert:  Jason replied 7 months ago.

To be honest i'l be loggin off in a few. We can pick this up in the morning if it works for you.

Customer: replied 7 months ago.
hi. morning is ok. but fyi water to top of fins is about 42cm and water to bottom of keel is about 42cm. So I'd say the fins are roughly in line with keel.
Customer: replied 7 months ago.
also - it's 2pm here. What time is it where you are so I know when morning is your time?
Expert:  Jason replied 7 months ago.

Good morning. Does the boat have a tachometer on it so that we can see what the top engine RPMS are with the boat going at full speed?

Customer: replied 7 months ago.
Hi - sorry for the delay in response. Yes it does have a tach - and revs at WOT when it's planing on smooth sea are between 3500 and 4000 rpm if I remember. I will need to check to be sure. I know this is much less than the rated max which I think is a little above 5000rpm. When it's in a choppy sea however - and not up on the plane - just ploughing - I can have it wide open but power flattens out and no amount of throttle makes any difference - it just dawdles along - but not sure what revs are then. Again I'd have to check which I could do this weekend.
Expert:  Jason replied 7 months ago.

Okay spark output needs to be checked in order to see if it's firing on all cylinders. Do you have a timing light to hook up to each plug wire to see if it flashes or not?

Customer: replied 7 months ago.
I'll need to check if I have a timing light. Used to. I might be able to borrow one. But again we're talking about the weekend. What are the steps that you are proposing so that I can get these done and report back to you in a couple of days?
Expert:  Jason replied 7 months ago.

All you would need to do is start the engine up, and hook up the timing light to each plug wire one at a time, and then hit the button on the light and see if it flashes or not. Flash means spark, no flash means no spark. Let me know if it's showing spark on all or not and we can take it from there.

Customer: replied 6 months ago.
Hi Jason, sorry for the delay. I connected spark plug testers to both spark plugs and both flashed with decent intensity. So there is spark present and it looks strong enough.
Expert:  Jason replied 6 months ago.

Okay so we have compression and spark. Click this link to pull up a picture, its one of the ones you sent me. http://f01.justanswer.com.s3.amazonaws.com/qcyTBAOV/BAD5C52B-A750-4A09-88E4-7A5260924FFD.JPG

Is the plate that the hydrofoil is bolted on to even with the bottom of the boat, or is it higher, or lower than the bottom of the boat?

Customer: replied 6 months ago.
Hi, the only way I could answer that accurately was to get the boat out of the water. Have now done this. The plate is about half to an inch above the bottom of the v of the hull.

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