6hp Tohatsu - 3.5 tonne Centaur - speed through flat water

Isn't the prop on Dylan's Tohatsu a significant factor? If it's a little prop for medium-sized tenders, we might expect that on a yacht, there'd be a flurry of foam for not much thrust...

...but if the prop is bigger and not driven so fast, I'd think the Centaur would reach useful pace - 5 knots - without much trouble. The depth (length of shaft) might have effect too.

The Centaur is substantial, but the little petrol inboards put in similar yachts 40 years ago hadn't much greater output than the Tohatsu. I can visualise five knots on the log.
 
Dan,

I agree - the Tohatsu is a ' saildrive ' prop optimised for pushing cruisers.

My 22' boat with an outboard well and slippery hull does 5 knots with a 4-5hp standard outboard.

When I tried the 2hp dinghy engine as ' Impulse Drive ' it barely moved the boat in a calm...
 
Giblets said:
Slight fredrift, D, but what is the reason for "digitising"? Do the cameras you use not produce digital output already?
Click to expand...

0uite a drift that is true

it has to be colour balanced, then converted to the format that makes youtube happiest, then the slow bit it has to be uploaded down our cronky old village connections to the outside world - an overnight job.

D
 
dylanwinter said:
0uite a drift that is true

it has to be colour balanced, then converted to the format that makes youtube happiest, then the slow bit it has to be uploaded down our cronky old village connections to the outside world - an overnight job.

D
Click to expand...

Thanks, all now clear.

Back to topic I would suggest 5.5 to 6 knots.
 
One of the things I wanted to do with ther well project was to try a centaur with a 2.5, 5, 10, 15 and 20hp outboard.

After seeing the 6hp push Harmony along it would have been intersting to see what would have happened with the Honda engines

a good PBO feature I would have thought

of course there are those who believe that outboards are not man enough for a heavy thing like a Centaur

D
 
Dylan-many years ago my brother was a member of an angling club that launched heavy clinker open boats off a shingle beach-IIRC Dungeness-where the maximum allowed power of the engine was 10 HP.

He was the envy of most other members as his Chrysler 10 HP two stroke would give him the edge no matter what boat he drew out of the hat.

The club owned the boats, the anglers supplied their own engines. The boats were drawn for by a simple lottery.

He was usually first to get out to the fishing mark. The Chrysler was an old fashioned simple engine with a heavy flywheel, and pushed the old fashioned open boats-about 18 feet IIRC-along very well, certainly better than most.

I found it for him. It had previously been used in a potting boat out of Ramsgate, again a real old heavy wooden tub.

It obviously had the correct characteristics and prop for the type of craft it was used on.
 
Seajet said:
Dan,

I agree - the Tohatsu is a ' saildrive ' prop optimised for pushing cruisers.

My 22' boat with an outboard well and slippery hull does 5 knots with a 4-5hp standard outboard.

When I tried the 2hp dinghy engine as ' Impulse Drive ' it barely moved the boat in a calm...
Click to expand...

When the head gasket blew on the inboard on a calm day on my previous boat, a 10m 3 ton X99, I used the Honda 2hp on the dinghy pushing the main boat to get me back in. 4.5 knots was no bother, not flat out on the outboard either. The only problem was stopping going through a lock. I'm not sure what Impulse Drive means with regards a 2hp outboard. I expect some space cadet type will be along shortly to inform me.
 
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Angus,

I was very surprised myself, the 2hp Mariner though a good little engine sure wasn't 50% of the Yamaha 4 or near that of the Mariner 5 I use now; presumably down to the prop.

The larger engines mentioned though not saildrive type actually are quite relatively large propped, I had to trim the blades slightly to get full revs...
 
Just 1/8" off the periphery, being very careful to keep it uniform on all 3 blades !

A bit ' suck it and see ' but it worked a treat; admittedly I was guided by my Father who is experienced with aircraft props.
 
dylanwinter said:
yesterday when the engine control grub screw loosened itself I was forced to put the Tohatsu on the back of the Centaur to get me home

would anyone here like to guess what speed half revs gave us through flat water?

I ran it in two different directions just toget an accurate through the water figure

I am digitising the film now and will post the answer to my question in the morning.

Dylan
Click to expand...

My guess ......... 6.2 knots
 
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