tohatsu 18 engine depth

[woz72]

I managed a few hours this afternoon..I cut two pieces of alloy sheet and used a piece of 30mm polyurethane machine packing and bolted it together I choose this route because I could easily strip and cut the packer down at different heights..

I used all six trim positions and hydro wing on and of for each trim and height setting...

130mm produced a lot of water coming into the boat travelling up the transom and cavitated on tight turns..

100 mm wasn't much improvement less water coming into the boat...

75mm no different from 100mm

50mm was ok still a lot of water

splashing behind the engine bit nothing being forced over the transom...at this point I took the extension plate off and sat the engine straight on original transom..4 hole away from the boat with trim with hydro fins fitted seemed to give the best results...

The 130mm setting seemed to put a lot of stress on the transom and in a way I was glad it didn't work at that height....the alloy didn't flex or look weak..my plan was to find the perfect position and then fabricate something more atheticly pleasing for a permanent fix....and questions help or advise greatfully receaved. I don't understand what's happened....

The was myself and my mate on the boat probably 35 stone combined weight....

[Locozodiac]

If that sib is not correctly inflated to at least to 3.0 PSI once resting on water for some minutes for pressure to stabilize, don't expect a good performance. Try to get a Zodiac pressure gauge as it's the only brand that will fit Zodiac's propietary air valves.

Happy Boating

[Locozodiac]

Woz,

To achieve good tube & transom rigidity. Was your sib well top inflated ?
Transom plate seems not well centered, probably just a photo issue ?
Did you visually check tail height passing throught water flow ?

Try removing doel fin from leg, that horse is very punchy, doel fins are used in most cases to help plane underpowered engines with badly ballanced sibs/ribs. I have finally found the proper place to store mine forever, the waiste basket.

As to understand Tohatsu water issues, check pic. Where are you right now. Is your 18 L same as in pic ?

Happy Boating

[Locozodiac]

If pic is not playing games with my eyes, you have a severe engine plate offset. That transom must have come as a staright one, previous owner seems have chopped it down a bit, including the installation of a probable small kicker at transom's ride side.

If that's so, you could play all week long with engine heights, trim setting with no aval whatsoever. You'll need to :

1-Fill in the chopped gap to have a straight transom by placing a wooden shim glued and screwed to transom (fastest way) done my a wood carpenter or yourself.

2-Center engine mount in middle transom, once there follow previous recommendations untill perfect engine transom height has been achieved. Check pic.

Happy Boating

[woz72]

Hi...sorry for not replying to pm or on main board....
The pics do make it look worse than it actually is...iv just looked at the transom and the cut out is indeed off center...ill reinstate it to make it leval and start the process again with the engine in line..with the tubes correctly inflated when the extension was at its highest it did seem to put to much flex into the transom...my zodiac is 1971 and I worry the it will put to much stress through the boat...with the engine at its lowest position it was doing 15mph using a Garmin GPS 60

[Locozodiac]

Don't worry, it's better to go slow and solve the tech issue forever. Are you inflating your sib by finger touch ? Any sib must have both tubes evenly inflated in order for engine to sit firm for sib to perform as expected. My ex 380 with same 18 was doing 20 with me alone on flat calm no wind waters.

Are your tube's seams and panel floorboards in good shape as to fully inflate it to it's factory recommended working parameters ? Have seen lots of inflatables with unglued transoms due to poorly inflation, engine rocks and ends stressing transom over time...

Happy Boating

[woz72]

Hi . The seams look in good condition and it holds air well..its just old and worries me lol..iv bought it to see if we take to the idea of sibs and next year I'll buy something more modern....I didn't want to run a duff engine and get into myther..