Engine Height

[raffles]

Hi Pros. The ride did seem better as Gofishin said. I'm in the process of putting the motor on a new boat I just bought, so starting from scratch again but I will be putting the motor 2 holes up from the start and see how that goes. Raffles.

[PROS]

Good to see this being stated (and correctly so) without you guys being shot down - like what was happening a few yrs ago on this topic, re what happens with the bow/boat trim due to a high or low motor.

What about if you drop the jockey wheel/hitch all the way down?

It's always a good idea, IMHO, to get 'a guide' of the start point when the A/V plate is parallel to the hull. Measure up/down and advise.

Yours is obviously a tin boat, with full transom (no pod). What sort of external keel does it have? I-beam, angle section (at 45/45), or half-pipe?

A single donk tin boat with keel will never be able to run as high a donk as a glass boat.

As a start guide:
Tin boat - A/V plate half way up the keel extrusion and go up from there, one hole at a time. My last tin boat (6m pressed 5mm bottom with external keel), I was able to go up to 25-30mm above the hull (can't remember exactly) but used a Permatrim (to counteract ventilation from keel), keel-cut, and a good SS prop.

Then it's down to water tests and visual inspection of where it runs in the water, as suggested by those above.

Even with a good alloy prop, you will not be able to run as high a donk as with a good SS prop. As Moonlighter has suggested, extra cupping can help - but prop needs to be a tad small in pitch to start with.

If your prop is bent/damaged/dinged etc, you will also suffer more ventilation (and even cavitation) than without prop damage, and a damaged prop will give problems with a higher donk where as with a low/buried donk it may not show up.

Mostly always better, except where bad design/build/damage/fit-out to hull causes a boat to tend to plough/bury the nose when running down hill. Then it is better to have the donk lower than where it should be - or better still, sell the boat .
Cheers
Brendon

image6.jpgimage5.jpgimage4.jpg

Outboard is trimmed down as far is it can go on the trailer, jockey all the way down.
Pipe is keel line. I would say anti ventilation plate is above the keel line.

Boat is not tiny or plate. Fiberglass Caribbean 21ft.

Max

[Chimo]

Max

Really hard to see heights and probably easier if pic is taken at rt angles across transom.
Also is it possible for you to drive the trailer wheels up onto some planks bricks or similar so you can lower the motor until the cav / anti ventilation plate is parallel to the bottom of the hull?

Cheers
Chimo

PS I never thought it was a tinny.

[gofishin]

...Boat is not tiny or plate. Fiberglass Caribbean 21ft.

Max

Hmmph, I would have sworn from the first pic that that transom looked ally with welded capping. Better go and see the eye doctor again, must be due for an upgrade .

As Chimo sez, depending on the start point, I would still go up one hole at a time, as this makes it easy when you reach/pass the limit to know if you stay there or go back down.
Cheers

[FNQCairns]

You might need to chock the wheels put the brake on and use a trolley jack at the front of trailer instead of the jockey to get the engine vent plate horizontal with the lower hull line.

raising the ob certainly does give good fuel and speed improvements for RPM it can also give one lower planing speeds and will help force extra hull trim to places it couldn't quite do before....ie like help eliminate proposing at certain problematic speeds with no other mods made.

But if lifted to get the most benefit it also makes for a lighter/flightier less reactive to driver input boat, one needs to be careful at times with all turns being slow arcs at higher speeds if raised to 'best' height. Tubing/sking also...forgetabout it if raised for offshore best trim and fuel usage v speed gains at cruise.

I had mine raised to it's absolute useable limit because my trips where often 40km+ each way and because of this it was no jet ski at any speed. In the end I fitted hydraulic jack plate to get the best of all worlds, because all boats not built solely for one purpose needs a range of engine heights every trip. The manual jack plates are also worth their weight in gold at the ramp....... rougher day offshore lower it, dead calm day raise it, tubing lower it etc.

or just set the engine to a mid range raise...will do nothing really well but nothing to badly either...90% of all boats I see at the ramp are too low.

good luck


Engine raise story .

Couple weeks ago at or near super moon tides I think. I was able to keep steerage against a strong outflow crossing a bar approaching it's low only because I could raise the engine to full height, otherwise I was going to need to wait 2 bloody hours min for the flood tide. made me happy being back home with a washed boat and drink in hand hanging with the fam instead of where I would still have been otherwise and in the dark.