splash back!

SiClapham · 09 August 2012, 11:27

I'm running an 18hp tohatsu short shaft on the back of my 4.2m zodiac classic mk2.
When opening throttle more than a gentle cruise, I get a heap of splash back coming over the transom - from the leg of the tohatsu

The pin is in the 2nd hole up, although there is no difference if in the 3rd up, boat loaded with 80% of weight forward (1 person and kit)

Any ideas how to stop with annoying splash?

lukewhiting · 09 August 2012, 11:46

This happened when i used to have my old small zodiac with a 5hp. i bought the engine height (not the trim) up a little which helped reduce it alittle. Might work for you too

willk · 09 August 2012, 12:51

It's been reported here before and seems to be common - raising the engine on the transom helps a little. Someone (mchappelow?) fitted a homemade "splash guard" on his which he said was a big help.

Locozodiac · 09 August 2012, 14:55

Quote:

Originally Posted by SiClapham

I'm running an 18hp tohatsu short shaft on the back of my 4.2m zodiac classic mk2. When opening throttle more than a gentle cruise, I get a heap of splash back coming over the transom - from the leg of the tohatsu :Any ideas how to stop with annoying splash?

Tohatsu's are prone to spash issues as described when engine is not height seated correctly on transom, it's a tail design issue. You could play with trim holes all day long with no aval. By the way, what's your transom middle height to lower hull/keel ? Is it less than 40 cm height ? To correct check following link under last post, just follow same procedures.

http://www.rib.net/forum/f50/cavitat...e-49596-3.html

Happy Sibbing

Zodiac Spindrift · 09 August 2012, 17:11

I get a wonderful cock tail in my 4.2 futura with a 20 Yamaha short shaft when doing over 18 kts, but very little comes back into the boat. Are you running a long or short shaft?

SiClapham · 09 August 2012, 19:14

Quote:

Originally Posted by Locozodiac

Tohatsu's are prone to spash issues as described when engine is not height seated correctly on transom, it's a tail design issue. You could play with trim holes all day long with no aval. By the way, what's your transom middle height to lower hull/keel ? Is it less than 40 cm height ? To correct check following link under last post, just follow same procedures.

http://www.rib.net/forum/f50/cavitat...e-49596-3.html

Happy Sibbing

Right, my transom is 37cm and some packers are cut for try-out tomorrow; bringing it up to the 40cm ish.
I'll post the outcome on here tomorrow evening

Thanks

SiClapham · 09 August 2012, 19:15

Quote:

Originally Posted by Zodiac Spindrift

I get a wonderful cock tail in my 4.2 futura with a 20 Yamaha short shaft when doing over 18 kts, but very little comes back into the boat. Are you running a long or short shaft?

It is a short shaft and an upgrade from my old johnston......which never suffered this annoyance; but then it never went this fast either

Locozodiac · 09 August 2012, 23:51

Quote:

Originally Posted by SiClapham

Right, my transom is 37cm and some packers are cut for try-out tomorrow; bringing it up to the 40cm ish.
I'll post the outcome on here tomorrow evening

Thanks

You need to shim rise that transom to be at least 40/40.5 cm height to work as expected. You could place a wooden shim screwed into transom to fill irregular shape so to have a straight transom. Probably will need to re position inside/outside motor pads height accordingly.

Happy Sibbing

Max... · 10 August 2012, 07:51

This seems to be very common - if you consult the manual and see where the anti-cav plate should be in relation to the bottom of the 'hull' then the engine will be too low, this is certainly the case when checking my Tohatsu 9.8 on my Zodiac 3.4m in the garage. Problem is the engine cannot be raised more than 20mm as the clamps will then not sit right against the transom plate.

wxmrich · 10 August 2012, 09:09

This happened with my new 18hp Tohatsu just last week. A 1 inch block of wood under the clamps has significantly reduced splash back.

Salty · 10 August 2012, 09:15

Quote:

Originally Posted by wxmrich

This happened with my new 18hp Tohatsu just last week. A 1 inch block of wood under the clamps has significantly reduced splash back.

Strange that I dont get any splash back with the old 16hp Tohatsu I have (the one I bought off Noah)

I'll take some measurements this afternoon and post them to see if the distance from the clamps to the prop / plate are different to the newer Tohatsu's.

Locozodiac · 10 August 2012, 16:55

Although all brands have short shaft engines, there are minimum differences between them, some engines will match perfect transom/tail height water performance other not, so shimming is the way to go/experiment untill you find the sweet spot height then you could finally arrange for an eye catching looking as in the examples.

Happy Sibbing

SiClapham · 11 August 2012, 20:22

Well, by simply adding a 25mm wooden shim......say bye-bye to Mr Splash-back

I could tweak some more; but this will mean adjusting the transom plate as the washers on the thumb screws at now up against the raised profile arpund the plate.

Transom height was 37cm.

Cheers for the pointers

Max... · 11 August 2012, 22:51

Peeps who have done this - any real increase in max speed?

lukewhiting · 12 August 2012, 11:10

Quote:

Originally Posted by Max...

Peeps who have done this - any real increase in max speed?

I think it all depends on the boat and engine. My thundercat engine's been raised but cause of the catameran hull it raises out the water along way anyway. When i raised the on the transom the revs picked up & i did gain some speed from it

wxmrich · 12 August 2012, 13:42

Quote:

Originally Posted by Max...

Peeps who have done this - any real increase in max speed?

No real increase for me. Air floor did seem to bulge less at WOT though. Another bonus.

Locozodiac · 13 August 2012, 17:01

Quote:

Originally Posted by SiClapham

Well, by simply adding a 25mm wooden shim......say bye-bye to Mr Splash-back

I could tweak some more; but this will mean adjusting the transom plate as the washers on the thumb screws at now up against the raised profile arpund the plate.

Transom height was 37cm.

Cheers for the pointers

Can you post pics of your final transom set up to see what you've done ? Would recommend to raise both engine plates to border if you hapen to have a plain border as in pics, that way engine clamps will be adjusted at middle inner plate. Raising the transom is only for solving water splashes issues at back transom forever which slows you down because of excesive tail drag against water flow.

If you could match transom shim height with water flow passing slight under upper small deflector plate would be ideal. Instant plane at wot, best top speed and perfect close turns at speed. Check video.

Happy Sibbing

SiClapham · 13 August 2012, 21:09

Quote:

Originally Posted by Locozodiac

Can you post pics of your final transom set up to see what you've done ? Would recommend to raise both engine plates to border if you hapen to have a plain border as in pics, that way engine clamps will be adjusted at middle inner plate. Raising the transom is only for solving water splashes issues at back transom forever which slows you down because of excesive tail drag against water flow.

If you could match transom shim height with water flow passing slight under upper small deflector plate would be ideal. Instant plane at wot, best top speed and perfect close turns at speed. Check video.

Happy Sibbing

So far, things are all temporary, I"m using a piece of softwood under the clamps. I might keep things like this for a while until totally decided on correct height required......but if shim is fixed/glued properly - I'll be stuck with the tohatsu!

Locozodiac · 13 August 2012, 21:22

If you think you'll be stuck with the Tohatsu, this is not so, all other brands have less tail issues compared to Tohatsu, this is not a malfunction, it's a tail design issue, so other brands like Yam will work fine.

Happy Sibbing