How Fast does ya boat go ! part 2

[Lucky_Phill]

OK, we'll try again.

Not too sure of the jist of this topic, but.

let's put up size of boat, motor hp with max revs and max speed. A lot of boat speed will depend on prop size.

Do we need speed ?

Do we need grunt ?

I believe we have to get the maximum " performance " out of a prop. Wether that be top end speed or holeshot.

There is also a big difference in GPS speed and the water wheel hanging out the back of the transom.

Go for people, and let's have a good response !

Cheers Phill

[mini696]

OK I'll bite...

4m centre console, 25HP and I get 18 knots average, but screaming and light on it goes at 22knots.

Also have an electric 50lb Minn Kota, get about 3-4 knots on flat water. Flat out I'll get a few hours from a deep cycle battery.

I wonder if I can get 25 knots if I run them both at once.

These speeds are GPS (across the ground), I dont have a tacho, or speedo, so I cant give many more details.

I would like a bit more power all round (holeshot and top end). I think the main problem is its an old motor, so it only feels sluggish.

But give me a bigger boat and I'll be happier.

Mickk

[dfox]

Wheres your boat phill?
Mines a 7 meter cat twin 115 yam 4stokes
max revs 5900
max speed on gps 36.5 knotts

[michael_k]

i have a 680 haines with 200 evinrude at 5600 doing 34knts.my 4m tinny does 25knts with 40 4st yamaha.the best part though i will be demoing a new nitro 901 cdx with a 200 optimax which will do 75 mph which aint bad for a fishing boat.

[pockets]

Posted this topic a while back but still not sure what good performance is, but

4.75 alleycraft 60 hp 4st
45 klm p/h @5100 rev

how far can you rev out a 60 4st?

[Cheech]

Wlcome to the site Michael. Have been out on a haines 680. Great boat.

[SeaSaw]

Welcome Michael .... 680 Haines .... Great Boat

Mine used to get 41 knots with a 200 2 stroke evinrude with a 12.5x19 prop and 38 knots with a 13.5x19 prop.

I now have a 225 4 stroke Yamaha and still haven't had it in flat water for full speed test but in a bit of heavy chop got 6000 rpm for 36knots with a 13.5x17 prop, but the motor was trimmed in a bit because of the heavy chop so it should go better than that.

All that is fine if you are water skiing, but the really important things are getting a good low speed plane, plenty of torque for heavy swells and a good cruising speed/fuel economy mix for offshore work. Top end speed realy doesn't mean much except to know that your engine is working in the right rev range.

Cheers,

Mark

[damons33]

mine is a 5.2 jbs 300mm half pod(2.4m wide at the transom)
17* deadrise, ae100 fourstroke yammy(4 carbs)has a 17" prop with a 19"pitch(not sure if that correct,will check it at work tomorrow)
she gets 72kms/6300revs with the wind on ure back and flatwater trimmed right out.
she planes at 18kms/3600revs and is very stable at this speed and holds her revs like a deso'
i would give nut left nut to be able to travel at 45kms everywhere(best economy).
i thinks it a great entery level offshore boat here a photo!
i feel safe as houses in this rig, i got a furuno 1650gps colour charty and l600 sounder. 60l plumbed bait tank,14ft riggers, 8 rod rack, digi troll4 down rigger and a ipcom vhs radio. ohh and a bilge pump

[michael_k]

mark , what revs was your evinrude doing with those props michael

[SeaSaw]

Michael, I wouldn't read too much into the top speeds as it depends on too many variables. The speeds I have quoted were in dead flat conditions in the Bribie passage, with the motor trimmed up as much as possible without ventilating, and only a little over 1/2 a tank of fuel.

The 13.5x19 prop was just right for the boat and reved out to about 5600.

The prop I called a 12.5x19 is a different story … it was really a 13.5x19 with half an inch of blade missing. When I bought the boat, it came with this prop on it. The guy I bought it from lived in Noosa and spend years taking it out through the Noosa Bar which is very shallow. Churning through sand had gradually worn a full half inch off the prop. That prop produced a great top end speed but it did over rev (I cant remember how high). Due to the lack of blade area on the prop, the boat had real trouble holding a plane at low speeds in any decent swell. ??? Needless to say, this prop was a dud and I replaced it immediately.

Cheers

Mark

[devocean]

Exactly the same as Mini

[ken4159]

5.5m JBS
115hp Tohatsu 2s
max. speed 33kn @ 5700 revs.

[blaze]

20 foot
115 merc, 62km
4.1 tinnie
4.5 merc slow (with the tide)
cheers
blaze

[michael_k]

MARK thanks for that ,i am currently in the process of playing with props on the haines.

michael

[skippa]

17ft Haines
115 Yammie