What Speed should i get

[soggy1]

Hi all i"ve just finished the complete rebuild of my Yamaha Southwind i've got a 115 suzuki 4st on the back i'm getting 5800rpm but only 55kmh just wanting to know anybodys exp with boat and what speeds you get i just thought i would of got a bit more speed then this Thanks Neil:)

[Crocodile]

Hello soggy1,

what does the boat look like?
Is a longboat style or deep vee.?
What sort of load do you have on board?
What size prop?
Have a look at Seamedia/ engine tests for a comparison.

[Willow1]

Hi all i"ve just finished the complete rebuild of my Yamaha Southwind i've got a 115 suzuki 4st on the back i'm getting 5800rpm but only 55kmh just wanting to know anybodys exp with boat and what speeds you get i just thought i would of got a bit more speed then this Thanks Neil:)
Hows it going Neil, You dont mention what size Southwind you have so I will guess that you have the 6.8 meter, as I have that size Southwind with a yammy 115 two stroke on the back. Fully fuelled, eskys, with 3 people on board I get 30 Knots 55km out of my boat. Thats the gps reading, empty tops out at 32 knots which is not much more than yours. Sounds like yours is very similar speed with the fourstroke. Cheers Shane

[soggy1]

Thanks for that willow now i need to get the triming right and maybe add a fin to try and get the nose down a bit Thanks Neil Yer sorry it is a ub 670 southwid just like willows.

[gofishin]

Hello soggy1,

what does the boat look like?
Is a longboat style or deep vee.?
What sort of load do you have on board?
What size prop?
Have a look at Seamedia/ engine tests for a comparison.Don't forget about engine height

[soggy1]

It has a long leg outboard which i belive is set down to far but with a fin this should help it is a southwind ub670 thanks Neil

[fishingrod]

We were running a UB670 as a rescue boat with a 115hp Yammy 4stroke EFI.

In a heavy rescue boat trim with clears, extra stainless work, tripple batteries, 100L fuel, bolt cutters, multiple fire extinguishers and lots of other stuff we got 33-36 GPS knots around 5500-5800rpm with 1-2 persons on board.

It had a Permatrim and Yammy stainless prop. Not sure on the pitch etc.

cheers
Rod


NB: The boat now has new owners and has been fitted with some small flotation pods on the rear + had some other structual mods and is now fitted with a 150hp Verado :)

[dogsbody]

If the motor is to far down now then a fin will possibly alter things (read dangerous). A fin if fitted should be out of the water at speed. Best way to go is get the motor height right first then go from there.

Dave

[Snapper88]

Have you had a chance to run the engine with improvment. did your top speed increase?

[soggy1]

Hi snapper no just had the wedge fitted today and a mate is coming over some time during the week to help fit the fin as i dont like to drill holes in anything to do with the boat but he does and gets great enjoyment from the look on my face as he's drilling holes in my boat as soon as the weather is ok again i'll be out Thanks Neil

[Moonlighter]

Hi Neil

Looking at the previous posts it seems that not too much is likely to be wrong. I honestly don't think that a fin will add any speed - in fact its more likely to have the opposite effect.

The first thing to check is the engine height.

Engine height has a huge impact on your boat's performance - acceleration, speed and fuel economy all impacted. In fact, you could already have the correct prop but if the engine is too low, it could be the one thing that is limiting your performance. Or you could find you can run a bigger prop and get more speed if the engine height is currently too low.

Some people will try to tell you that you can look at the back of the boat when its on the trailer and tell for sure if the motor is at the right height. That's simply not true.

See this link, it really is worth a read and a look at the pics:
http://www.veradoclub.com/smf/index.php?topic=137.0 (http://www.veradoclub.com/smf/index.php?topic=137.0)[

It includes excellent pictures taken when the boat is at speed to show you how a cav plate looks when its too deep and when its at the right height. It also tells you in very precise and easy to understand terms how to determine if you have a prop fitted that suits your boat/motor.

Note the expert's advice that getting the engine height right before doing anything else is critical.

Hope this helps.
Cheers
ML

[soggy1]

Thanks moonlighter, my only prob is that i cant lift the outboard any higer it was fitted by the boat yard that i bought the outboard from so i havent done this myself, but the top bolt is only a 1 1\2" from the top of the transome cut out and its on the bottom hole. So i was told by the boat yard that a fin would do as good as liffting the outboard 1 hole on the back so i'm only working of what they have told me, i've never owned bigger boats before so this is a bit new for me Thanks Neil.

[Moonlighter]

Hi Neil

Personally I think adding a fin has nothing to do with it. Fins are mainly used to improve stern lift during take-off or on boats that are a bit ar#e-heavy. Or to help stop porposing.

Can't see them adding any value at all if the motor is too deep - in fact it would most likely slow you down even more and could be quite dangerous - they can dig in on sharp turns with unpleasant results, to say the least, if too deep.

Once on the plane they should be on or above the surface and apart from maybe inproving response to trim, they then do very little.

Have you done the test as per the Verado website instructions? If not what have you got to lose - do it and see what you find. Until then I'd do nothing if it was me, certainly I would think very long and hard before probably wasting time drilling holes in the cav plate and fitting a foil.

Maybe you are focussing too much on top end speed. Virtually never use full throttle full speed anyway.

Cruising speed is much more important, as is the ability of the prop to keep you on the plane at lower speeds in crapp# conditions and also the ability to get you up on the plane nice and quickly. If yours is doing that stuff well, then be happy!

If you really think its underperforming or are not sure, take someone experienced out with you and get a second opinion. You might get a surprise what they say.

Cheers

ML