Boat setup problems

[New_fisher]

Hey guys, I am having a ridiculous amount of trouble getting the boat setup correctly :'(
I have a 4.1 ally craft rhino with a 40hp yammy two stroke on the back. It used to throw the nose skyward when I tried to plane :o so I put a stingray foil on, seems to be working ok but now there is a $hit tin of spray coming off the foil - Is it supposed to be underwater when travelling at top speed, or shoud it be just skimming the top of the water - I was thinking of raising the engine so that the foil will be on top of the water hopefully this will fix these problems -
1. lower top speed due to the drag from the foil being under water,
2. spray pi$$ing off the top of the foil when on the plane,

The only concern that I have is that if I raise the engine up high enough so that the foil is just skimming the top of the water, she will cavitate like a b!tch,
Appreciate your help guys?
Regards Hurlz

[nevd]

If you have a good prop, preferably stainless with some cupping, you should be able to run the AV plate and so your foil above the water surface at high speed. The more damaged the prop, the lower you will need to run it to stop ventilation. As a general rule, motor should be mounted as high as possible consistent with still getting reliable cooling water supply and being able to live with the ventilation in turns.

[New_fisher]

When you say cupping, do you mean curvature of the prop blades?

[New_fisher]

How high should I have the motor on a aluminium tinnie? Has anyone thought of putting spacers between the cav plate and the foil to change the angle between the twol? I was thinking of putting a few spacers under the front two holes of the foil to lift the front of the foil up, thus giving it more lift - has anybody tried this?

[Mantaray]

before you do anything more, what's the relationship of the cav plate to the bottom of the hull now?

[sf17fisherman]

also what posistion is your trim in??

to me sounds like you have too much trim on the boat hence hard to get onto the plain and now spray off the foil

both things may be able to be fixed by droping to motor down one trim posistion ;)

[New_fisher]

the boat gets onto the plain pretty easily, the trim is on the third hole from the bottom, but when I put in a hole lower the boat seems to run with the nose pretty low in the water, also the cav plate is about 1 inch below the hull. Any thoughts? ;)

[iank]

I think the cav plate should be at least level with the botom of the hull.
Ian

[sf17fisherman]

yeh trim sounds about right and could even go up one to the fouth hole

i would agree and the motor needs to be lifted till it is atleast level with the bottom of the hull if not a tad higher

what could be happening is the hull is getting too far out of the water and you almost rideing in the cav plate
raise the motor one hole and things should ride more levle

[-Sharp]

when you plane, how much of the craft is supposed to be out of the water? :-?

[sf17fisherman]

depends on trim and conditions and a heap of other things but a nice amount would be 2/3rds

[nevd]

When you say cupping, do you mean curvature of the prop blades?

Yes, cupping is curvature of the trailing edge of the working face of the prop. It is not normally fitted to small outboards or low pitch props on large outboards, but is normally present on a high performance prop. Cost of cupping with correcting pitch errors and blade sharpness is approx $100 so it may not be worthwhile on a damaged aluminium prop, but is money well spent on a stainless prop.

Cupping will allow the motor to be run higher. Running the motor higher will increase speed, decrease fuel consumption and decrease steering effort and allow the boat to run at a lower trim angle ie flatter without having to trim the motor in. Foils on outboards can (but not always) give some nasty handling problems and this is most likely if the foil is not above the water surface at high speed. If you get the motor up, it is unlikely you will need to pack between foil and AV plate.

[New_fisher]

has anyone ever put spacers between the cav plate and the foil so that the engine doesnt cavitate but the foil is above the water? any success? Cheers Hurlz

[Spaniard_King]

Hurlz.. can ya give us a side on picture of the cav plate and bottom of the hull with the engine in the position you normally run it at.

Be handy instead of everyone guessing ::)

Garry

[New_fisher]

Yeah sure Garry, great idea, will go and do it now, should be up within half an hour, thanks Ray.

[New_fisher]

Here it is boys, note the cav plate is pretty much the same height as the keel, your advice is appreciated, Ray.

[New_fisher]

two, the cav plate is almost in line with the keel, the guy st the boat shop said that the aluminium boats cause more turbulent water off the back due to the chines, therefore you cant lift them as high or it will cavitate, sound reasonable?

[New_fisher]

Final one

[Spaniard_King]

two, the cav plate is almost in line with the keel, the guy st the boat shop said that the aluminium boats cause more turbulent water off the back due to the chines, therefore you cant lift them as high or it will cavitate, sound reasonable?
Nope :exclamation. Your engine is way deep in the water.

I would lift that engine 1 hole..possibly 2. It would be a whole different boat with it lifted. Cavitation shouldn't be a problem.

Being an alluminium boat it will be easy to lift. 10 min job to lift, if ya need a hand gimme a yell, will come and help ya ;)

Garry

[blaze]

Like garry I reckon ya wanta go 2 holes though, there must be a lota underperforming boats out there. Maybe the dealers set them that low for beginners, like having L plates and restricting speed.
cheers
blaze

[suttos]

I had a stacer that would bow steer when the motor was set close to the transom. The cavplate and the foil should be somewhere near the bottom of the hull. Remember that the foils job is to help you get out of the hole and prevent cavitation when turning. It cannot do this if the foil is above the bottom of the hull line.
I would try some spacer washers, you have nothing to lose to get rid of the spray.
As for hull speed its a balance between bow steering and top speed.

[rajawolf]

Hurlz,

As Gary said mate if you need a helping hand to lift it...I can come and help you also.

Cheers,

Tony

[New_fisher]

Guys thanks for your help, I have already lifted it one hole already - if I took the pics last week it would of been another inch lower again, I will pull it up another hole - I only have one hole left - what happens then? Do i have to drill more holes in my transom? If I get stuck I will give you a yell - thanks very much for the offer though, Cheers Ray

[youngfisho]

hurls,

have you run the boat yet?

how does it perform?


andrew

[New_fisher]

nah mate, crook as a dog. probably put her in tues next week, I'll let you know how she goes, I was thinking of buying some of those plastic cutting boards used in the kitchen and cutting a few spacers out of them to lift the foil off the cav plate - anybody got any better ideas? I thought the plastic wouldn't mark the paint on the engine and would slao stop corrosion? thoughts?
Cheers Ray

[blaze]

Hi Ray
I personly dont like any of the add on wings, if outboards were meant to have such a beast they would be part of the original moulding and not an odd on feature to mask a possible fault/poor design or under powered hull.
One of the reason I dont like them is it puts tremendus pressure on the orignal cav plate (not that I have even seen one broken for this reason), by putting spacers under the wing to raise it in the water that leverage would be increase dramaticly
Just my humble opinion
cheers
blaze

[youngfisho]

mate put a foil on his 25hp and didnt really notice too much of an improvement. But i have a foil fitted to my 70 johno and people have commented how quickly the boat gets on the plane. Have not tried the motor without it but the previous owner noticed better trimming and quicker planning when it was fitted to his first motor a blue band merc.


andrew

[speedy]

i say scrap the foil chuck a trophy prop on and lift her up
about to do that to mine ill tell how the prop goes cheers

[New_fisher]

Thanks Speedy, interested to see how you go - what is a trophy prop and what advantages does it have over the factory prop? Cheers Ray.

[Seahorse]

i have a 4.2m stacer with a 30merc, it was on numb 2 hole out and at the end of a day my shoulder was just aching. i put up with this for few months, then last weekend put motor out to 3rd hole and it was like have power steering, but just seemed to dig in a little longer on takeoff. but it does throw more water up at the back. i was going down in morn to buy a $25 foil and see if it makes a difference to getting out bit quicker. but steering is really easy now, can move tiller arm with one finger as before had to hang on real tight.

[New_fisher]

I put the foil on top of some spacers, but it didn't make a lot of difference, and the donk seemed to cavitate a bit, so I dropped the foil back down to where it should be - this is with the donk lifted one hole on the transom. She runs pretty well, I have put a different prop on it (both Yammy props) from a 12 to an 11 - the revs are a bit healthier 5500. I think that's all I'm gonna get out of her - 32 knots, not blistering, but not bad, does this speed sound right? thanks for your help fellas, till next time, Ray.