# Outboard trim angle



## Brett (Jul 16, 2008)

I've noticed many of the pics of small boats posted here
( those without t-n-t ) are mostly set up with the engine tucked under.
Just curious, what's the reasoning behind setting your thrust angle downwards?
It would seem to be a waste of power to vector the energy down, instead of opposite the direction of travel.

Example:


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## Gramps (Nov 1, 2007)

My trim is set with the thrust down slightly, sorry Brett no protractor handy.  Main reason is due to the weight in the rear of the boat; 115lb outboard, ~36lbs fuel, 50lbs of battery, and me. Need to get the bow down/transom up.


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## Tsport (Jan 4, 2007)

I have a porposie problem when I try and trim my motor. Once I have tabs on the skiff I plan to revist it again.


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## Brett (Jul 16, 2008)

So you're converting gasoline to lift, and losing speed off the top end?

Might be time to rearrange the furniture...


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## Gramps (Nov 1, 2007)

> So you're converting gasoline to lift, and losing speed off the top end?


Yes sir.  It would be best suited to move the gas to the bow and the battery to the mid box.  But the electric is already rigged under the rear bench and I'm too lazy/cheap to move the gas.  Besides going ~30mph is plenty for me.


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## Brett (Jul 16, 2008)

> Besides going ~30mph is plenty for me


You say that like you expect me to believe it... ;D

We all feel the need for speed sooner or later! [smiley=carcrash.gif]


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## mark_gardner (Mar 18, 2009)

i dont have a jack plate but do have to have the pin on the lowest setting even with the sting ray while riding solo, if i bump it up one hole i lose about 1or2 mph's i do have a pretty good hole shot though


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## tom_in_orl (Dec 9, 2006)

I am in the center pin and the motor is close to being vertical when the boat is level. Answer for why is simply that where it ran the best during testing while driving solo. With two people in the boat. I can put the pin in the next furthest out hole and run just as well. In fact if I would remember to do it it would probably run better in a chop. Usually I just have my passenger sit next to me instead.


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## WhiteDog70810 (May 6, 2008)

I concede that you could balance your hull perfectly, set the motor to the perfect angle of trim and minimize the hole shot.  However, the variables will ruin your plans.  Every gallon of fuel, bag of ice, 12 pack of tasty beverages, fish in the cooler and lead-butted buddy will destroy your perfect arrangement.  

Even with a hull that is perfectly balanced at its running angle, the perfect angle of trim will probably fall between those damn pin holes.  With a small motor that is either up or down without an infinite number of angles of trim in between, it is simply easier err on the side of caution and set the motor low in order to consistently pop it up on plane regardless of load without 200 yards of nose high wallowing or porpoising.  Also, if you are running a motor that is a touch on the small side for your boat, an extreme angle of tilt may be required to get the average stern heavy boat onto plane and keep it there.

Why are boat stern heavy?  I think it increases the motor's ability to get a given load up on plane.  A motor can pop an heavy load up on plane easier if the weight is in the stern and the bow is light.  I have seen heavily laden (okay, overloaded) boats fail to get on plane if the weight is balanced along the length of the boat, whereas the same rig can handle the same weight if the majority is in the stern.  Like I mentioned, this seems to only apply when you are really pushing your boat's capacity, but manufacturers hedge their bets and place fuel and batteries to the rear and sacrifice some draft.

All those factors lead folks without power trim or trim tabs to set the motor low and never touch it again.

My $.02.

Nate


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## Brett (Jul 16, 2008)

If tucking the motor in is what keeps you safe, it makes sense. Better an engine vectoring thrust downward than a hull porpoising.
I've been testing angles and mounting heights with different loads on my hull and found that holes 3 and 4 give me the best speed and ride.
Anything further up than 4 ventilates the prop, lower than 3 produces considerable drag and slows the boat down.


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## anytide (Jul 30, 2009)

well said Nate...  my  little wood skiff has a 15 degree angle on the homegrown jackplate already ,then tuck motor all the way to last pin hole will put it on plane in its own length  under light load w' 25 hp, and great for skinny water cruising  at slow speeds then adding hydrofoil or giant cav.  plate allows for even better hole shots, i put giant fixed trim tabs in the hull design for my version of the best skinny skiff  its great for cruising @ slow speeds looking for fish


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## anytide (Jul 30, 2009)

tucked under-testing for HOLE SHOT set-up :


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## choppercity47 (Jul 30, 2007)

I have a 6 hp on jackplate and i lose power, hole shot, and running depth if the motor is not tucked all the way in the last pin hole. 

Only time I trim it up is to surf into white caps.


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## LoneRanger (Dec 11, 2006)

solution: factory tilt and trim!


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## Frank_Sebastian (Oct 15, 2007)

An easy way to think about thrust vectoring is to consider the very common 3 point hydroplane. (a venerable old racing style boat) There you have two sponsons on the front and the step in the rear. Three points determine a plane so if all three planing surfaces are balanced (not equal) the boat will perform at the most efficient angle of thrust to supporting surface. If you should apply this to the Gheenoe hull you would add a hydroplane at two points up front and a step in the rear. Once up the boat would run level and at its best with a very hard ride. (good for the liver, but back and kidneys will suffer)

Trim tabs and motor angle (trim & tilt) offer a quick and simple solution to pitch control although it comes at a small price of reduction of efficiency.

Boats like the Carolina Skiff use a single very large planing surface and can plane large loads with modest horsepower. (i.e. like a lightly loaded wing in a plane designed to carry cargo) They are not as sensitive to loading as the narrower spindle profile with narrow transom of the Gheenoe. I would try to balance the load as well as I could, but often there are social reasons to not do so. That is a great reason for trim and tilt. I don't have it on some of my boats, but then it is usually just me and some dead fish to complain about where we have to ride.

Best regards,
Frank_S


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