Low speed planning performance.

[cormorant]

Andy,

low and mid range torque is what outboard manufacturers are all after, it plays a big part in low speed planning. The more torque down low an engine has will hold a boat on the plane at as lower speed. As Smithy has suggested the 2 stroke tends to fall off the plane earlier than the 2 stroke.

If the 2 stroke was propped for performance at that those revs for low speed planing rather than top end it wouldn't suffer that. It would suffer somewhere else unless hull and prop were 100% matched - yeah that rarely happens. A 2 stroke has more torque and reserve torque at just about all revs( especially low ) in general but how it is propped ( what gearbox) and used is the other half of the problem. Since the torque graphs for comparison use revs over torque one being higher than teh other at specific revs means nothing unless the prop and hull can use it effectively. If manufacturers would like industrial diesel motor manufacturers put out decent data it would be a help in motor selection for specific purpose as a general outboard is a compromise for different uses.



A 2 speed gearbox would make all the difference or a prop that pitched out at really high revs to give that top end ( yep they exist- 2 speed props for ski boats )
Basically a lot of motor issues are actually prop issues . Some hulls are not designed for a slow plane with the boat at a good attitude.

The way people load their boat up with extra weight these days I'm amazed some plane at all. Assumably later hulls designed with 4 strokes in mind and with live bait tanks from teh factory have taken that into accont but retrofit boats?

A prop is always a compromise and very few people prop their boat for mid range performance as they don't want to lose their top end ( wank) performance that is used for possibly 5% of engine hours unless ski racing.


Still amazes me the same motor with the same ports , cam is used for both skiing and offshore lugging and yep electronics can fill the gaps but that comes at a price.


Low speed planing - longer hull- hull extensions, pods, trim tabs , permatrims can all help if set up right.

People above have covered most all of the options. 4 Blade props that add stern lift can help but they can cause handling issues at higher speeds if it is overdone.

Ok so who is for a diesel with a 2 speed box or variable prop??

[Micadogs]

Hi Big E,

I installed trim tabs on my boat and my 'slow plane' speed dropped from approx 25-28 klm / hour to around 16 - 19klm / hour. They also straighten the boat from wind list which makes it a much softer ride. My 8 month pregnant wife and a 2 year old slept all the way home from tangalooma to manly in a 20 knot wind - no banging and crashing etc

Trim tabs made a huge difference to my boat - both slow plane and slapping.

FYI - 5.5 metre fibreglass boat with a 115HP 4 stroke

Regards Adam

[TheRealAndy]

Andy,

low and mid range torque is what outboard manufacturers are all after, it plays a big part in low speed planning. The more torque down low an engine has will hold a boat on the plane at as lower speed. As Smithy has suggested the 2 stroke tends to fall off the plane earlier than the 2 stroke.

How? The only way I can mentally picture this working is by using torque to somehow provide extra lift? If this is indeed the case, then best way would be to use 2 engines with foils?

[Noelm]

twin engines will maintain a slower plane.

[Chimo]

Hi Corm

Yes please, I'd like a diesel with a 2 speed box or variable prop for when I have to change over from my twin 115 s outboards but I suppose you need me to change boats too?

Cheers
Chimo

[TheRealAndy]

twin engines will maintain a slower plane.

Ok, so then to get even more lift from your outboard, would you not also be better off using high thrust props/gearboxes (knowing that you will lose top end speed)?

I am still not sure I get the whole concept just yet though, to me it still does not make a whole lot of sense. Everytime I picture it in my head someother concept comes and destroys it for me

Also, I am not sure that the whole 2 stroke v 4 stroke thing would make a whole heap of difference. Surely the torque at lower revs is not that significantly different to make a big difference. I would guess that prop selection would be much more important.

[Jabba_]

If there is such a thing as "usable torque" 4 strokes have it and 2 bangers don't. The Etec advertising rabbits on about how much torque they produce but in the real world a 4 stroke will keep you on the plane at whatever rpm you want, especially if you have a foil on it and the 2 stroke will want to jump up and race away on you once it gets the hull planing. Same downsea, the revs will go up and down a lot more on each wave or swell with a 2 and may only change 300rpm or so with a 4 stroke. My motor for instance I am usually running at 4,200 rpm to keep it up on clean plane and a big swell can knock me back to 3,900rpm but I will still keep on the plane without touching the throttle then I might race away to 4,200 on the down face of the swell but it won't race away like a 2 stroke would have.

I can't vouch for any other E-tec but mine on my rig, I dont get any runaway unless it is a real steep wave comes along and stands the stern up high...

However if I have not trolled for a long time (between seasons) the motor will for the first 5-10 minutes (when running with the swell) will want to run on.. After that the EMM learns and adjusts to my driving style or trolling and very rarely will I need to make another adjustment to the throttle, unless I get a biggy stand the stern up. But even then a 4st will run on also...

My prop made a big difference also.. My original Viper was great for high speed, but not so great offshore or slow planing..

I now have a Rebel, it can hole a slow plane very well at 2500rpm on smooth water and 2800rpm offshore.. Top speed lost 2mph with this prop, but erveywhere else is so much better...

[oldboot]

Apart from very small changes that foils, trim tabs and engine choice can have.

There is only 1 thing that will consistently improve low speed plaing on a given hull.......and that is weight distribution.

All the other things.....the slower you go the less influence they will have.

weight distribution will effect hull performance at every speed.

Include in weight distribution weight reduction.

prop choice and all that will have very little effect on what speed the hull will plane at.....all it may do is allow a more consistent low speed to be maintained.

for example.
My BIL's little savage with 30HP on the tail and no trim facilities.....with 3 aboard, moving the two pasengers forward a couple of feet forward makes a huge difference to how easily it will plane and how slow it will plane..with one aboard up front, it will stay on the plane at rediculously low speeds..it is sweet, well ballanced and light.

My Stacer with 60hp a pod, electric trim and foils on the other hand was far too stern heavy, realy had to climb out of the hole and would drop off the plane quite early.
All because it was heavier and poorly balanced.....hopefully better soon.


before you start spending serious $$$.
Look at how the boat is loaded and perhaps move some things like people, eskies, batteries and fuel tanks.

cheers

[Noelm]

high thrust gearboxes (that is lower gear ratio) enable a bigger prop to be used, and turned slower, which does result in better low speed plane (kind of like your car in 1st or 2nd gear) but it is a compromise (as always) 2 strokes do have a very defined "power band" and some will go like the clappers once this band has been reached, but will die off if the RPM has dropped just a tiny bit below it, anyone who has ridden a 2 stroke dirt bike will know what a power band is, thats for sure.

[bigjimg]

BigE I have fitted a Stingray foil,similar to a permatrim,and can maintain planing at 10knt.Made a huuuge difference to the handling,all for the better,and keeps the bow dead flat when getting on the throttle.Very cost effective alternative to trim tabs,I was considering them but now I won't bother.Took me 15 minutes to install and no holes to drill.Jim

[Tickleish]

Hey Jim,

Where did you get your foil from & how did you not have to drill holes?

PS I've got the same donk as you.

[bigjimg]

Hey Jim,

Where did you get your foil from & how did you not have to drill holes?

PS I've got the same donk as you.

I got it from Whitworths,was $249.You take the cavplate anode off and then the foil slides on over the cavplate.All that needs to be done is bolt the anode back on into the recess on the foil which clamps the unit onto the plate,job done.Jim

[marty666]

you can buy the same foil from cabelas for the $100 mark plus postage which would be half the price here that is where i am going to get mine from

[robothefisho]

Props WILL make a HUGE difference to slow speed planing ability.

Suzuki 140 plate boat 3 blade, planed to around 12 knots maybe a little less.

Same boat, 4 blade prop same pitch, holds plane at 7 knots.

The difference is the thrust delivered. Mind you planing at 7 knots is not at all economical as it's still revving at 3000 somthing.

[BigE]

Lots of information to sort through , thanks for taking an intrest, I would like to hear more opinions on 4 blade props pros and cons. and about an engines ability to hold on the plan without to much throtle jockey work , Im a set and forget and enjoy the ride type of boater.

So far I'm thinking 4s with cubes some wedges and maybe a 4 blader.
any thoughts on this combo?

BigE