Help with outboard height

[doggy39]

Hi just after some help have fitted a 40 four stroke tiller(gas assist) to my sea Jay 4.35 with the motor trimmed out and level the cav plate is about 15mm under the hull I am having problems staying on the plane at low speeds now Un like the 40 2 stroke I had with a fin, would lowering the motor 1 hole make any difference and what does lowering and raising a motor do please, I am looking at putting a fast tail on it to solve coming of the plane so early .should have got the power trim but that's another story.Thanks

[Moonlighter]

The Verado Club has an excellent article on engine height, what effect it has, and how to get it right. It applies to all motors, not just mercs and is widely referred to when people ask this question. The guys who provided the info are prop experts so they know what they are talking about.

http://www.veradoclub.com/smf/index.php?topic=137.0

[scottar]

One thing I have found in relation to outboard height and pressed tinnies is that to prevent prop ventilation through cornering with any sort of trim apart from fully down, the outboard needs to be a bit lower than it would on a glass boat or platey. I can only assume this is due to the "keel" taking water away or creating sufficent disturbance through the turn to effect the water flow over the prop. I messed around for ages with a 4.5m Savage that I owned - motor up/ down, foil on off and ended up with motor slightly low and foil on. However, every hull is different so try adjusting your motor height first as it is cheap and easy to do but I suspect from my experience you will end up fitting the foil to achieve a slower planing speed. The only other costt effective option may be transom wedges to allow more negative trim angle. The no expense spared option would be trim tabs or having flotation pods/planeing extensions fitted to compensate for the extra weight and removal of the old foil.

The foils do create drag. On my Victory I have been messing around trying various options as well. Tried the SE Sport - WOT RPM dropped significantly enough that I would have required a prop change. Fuel economy dropped but the stern lift did make the boat plane a lot slower. Next port of call was the Permatrim. Drag was still evident - RPM drop was about 200RPM so nowhere near as bad as the SE Sport. Ultimately I took the foils off and fitted tabs. As such I had a good look around when I wanted a foil for my tinnie and ended up with a Solas Laser Foil. They are made from 3mm stainless. My thought process was that as I knew the foil would be running under water so I wanted the thinnest material possible to minimise drag. I have isolated the foil from the ventilation plate with high density plastic washers and it did require a sand and buff to remove some sharp edges. Apart from that all is good.

[doggy39]

Thanks Scottar for the info , Did you use the washers for the reason of electrolysis.

[scottar]

Yeah, galvanic corrosion. Also used a heap of the duralac on the washers and bolts. If you dont have any anti corrosion compound, Tef-Gel is the nicest to use. I already had the duralac. The crap gets everywhere.