aqua lark not planing

[modman]

thanks guys raised the engine boat comes out of the hole and it screws just need to float the rear up a little now adding tach si will know whats going on then time for all the mods

[phillnjack]

First of all the boat is very short and it will never ever get out of the hole fast with anything bigger than a 15hp.
i had the same problem with a 30hp on a apollo 9ft 6in boat.
A15hp being so much lighter lets the stern get up quicker.

Now go get a set of doel fins and put them on the engine and see the difference.
Trim it in a touch and the bow will try to plough,trim it out and you see the sky ha ha
these little boats need to be just right.

you will never get 50 with a 25hp johnson engine on that boat unless you spend thousands, and i doubt very much a 40hp would do it neither.
so many people think they do 50mph, when infact most are barely touching 40 !!!!!!!!
the boat was not designed for such high speed.
the best i got from a suzuki 30hp on the apollo was 34mph and that seemed like 100mph in that little boat.
once it got over the hump it flew like a little bat out of hell.
with 2 people it took ages to get on plane.
I used mine on the river and at sea in some hairy waves, it was a blast but very hard work
keeping it in a straight line due to chine walk.

The engine being a long shaft is a big disadvantage as it makes the boat top heavy at the aft end and can cause a torque problem on such a small boat.
Look around for short shaft, it realy will make a big difference to the handling.

you will have massive amount of fun with the boat though, i enjoyed scaring myself silly with the little apollo ha ha


these were just my observations with using tiny micro speedboats and bigger outboards than they were meant for.

phill

[modman]

ran the boat 42 mph on gps with 16 pitch stock aluminium prop its a 40 hp yamaha 3 cyl doing reeds head lightweight flywheel and exhaust and a ron hill 12 /20 cleaver next and then see what happens i will get it up to 50

[phillnjack]

The gear ratio of your engine is 2.00 - 1 ( presuming this is not a special ratio you have on the engine)

Max revs of the engine is around 5,500 (unless this has been hotted up)
that gives you 2,750 rpms at the prop @2.1 reduction .
the prop has a 16 pitch ,
so in theory without slip this would travel 16 inches on each revolution of the prop.

Ok lets see what this realy would be in the imaginary world of no slip props.


Its very simple mathmatics to calculate theoretical speed with no slip at all.
The rpms are 5500 at the flywheel,
the gear ratio 2.00-1 so its half of engine revs =2750
so we have a pretty easy starting point.

2750 rpms per minute, x 16 inches per minute. = a speed of 44000 inches per minute
divide this by 36 to give yards and you get .= 1222.2 yards per minute.(36 inches = 1 yard)

Now 1,222.2 yards per minute x 60 to give you how far in 1 hour = 73,332 yards per hour. There is 1,760 yards in a mile
so just divide 73,332 by 1,760 to give miles per hour.= 41.66 mph.

This is only theoretical with NO SLIP AT ALL and no drag from the boat ?

Maybe you have a special race engine





phill..

[fs5]

the 3cyl 40 has a 1.85/1 gear ratio mate.

[phillnjack]

1.85 --1. gear ok

theoretical maximum speed would be 45.7 mph. with engine running at WOT 5,500 RPM
that is without any drag, any slip , mirror glass water !!!!!!!!!!!



phill

[modman]

ok so ur telling me gps is wrong

[capnzee]

The GPS only tells you the speed you are doing over the earth, ground etc. If you are running downstream with a current of 10 mph, your GPS will include the speed of the current plus the speed that the boat is running. eg. boat speed 32 mph, speed of current 10 mph resultant speed 42 mph. A GPS reading is only accurate over "dead" water as in a small lake with no movement. Rod

[capnzee]

see my answer below****

The gear ratio of your engine is 2.00 - 1 ( presuming this is not a special ratio you have on the engine)

Max revs of the engine is around 5,500 (unless this has been hotted up)
that gives you 2,750 rpms at the prop @2.1 reduction .
the prop has a 16 pitch ,
so in theory without slip this would travel 16 inches on each revolution of the prop.

Ok lets see what this realy would be in the imaginary world of no slip props.


Its very simple mathmatics to calculate theoretical speed with no slip at all.
The rpms are 5500 at the flywheel,
the gear ratio 2.00-1 so its half of engine revs =2750
so we have a pretty easy starting point.

2750 rpms per minute, x 16 inches per minute. = a speed of 44000 inches per minute
divide this by 36 to give yards and you get .= 1222.2 yards per minute.(36 inches = 1 yard)

Now 1,222.2 yards per minute x 60 to give you how far in 1 hour = 73,332 yards per hour. There is 1,760 yards in a mile
so just divide 73,332 by 1,760 to give miles per hour.= 41.66 mph.

This is only theoretical with NO SLIP AT ALL and no drag from the boat ?

Maybe you have a special race engine

****If you want a real easy way of figuring your speed at 100 per cent efficiency (you will come within a mile or two of the way you figure it)::::subtract 1 inch from the pitch of the prop, in this case it is a 16 inch prop so use the number 15 and multiply it by the rpm of the prop 2992 (assuming engine is running 5500 with a 1.85 gear ratio) result will be 44.59 mph. Not too far off when you are in a hurry(within 1 to 2 percent) and not figuring the drag. Most modern props may be called 16" but in reality, this is an average pitch measured through a specific area of the prop. It may be more than that near the hub and it may be less than that at the tips, a little "cup" also changes the resultant pitch--in other words all of this scientific **** is not worth much except to start arguements. Results are what counts. Go for that 52 mph, you may or may not get it but will have fun trying. Rod



phill..

[fs5]

42mph is about right for a 16p alloy prop on the limiter.thats about 12% slip ,wich seems about right for a alloy prop .
modman to run a cleaver mate ,you going to have to jack your motor as high as it will go and still suck water.if you can swing the cleaver and hold your boat on the water you will get way over 50mph