approx outboard speeds question

[The Fuzz]

Hello all,

I know that varied hulls etc will create a grand difference but what
are the approximate kt top speeds of:
30hp
40hp
60hp
85hp
100hp etc
outboard engines when placed on your average 17ft speed boat.

I''ve scoured the web to find some sort of comparision chart and now
throw myself at your mercy.

Cheers.

[trainfan1]

The Fuzz wrote:

Fiberglass, aluminum, wood, plastic? Weight of boat? 4 stroke or 2
stroke engine? Weight of persons, fuel & gear? What do you want to
accomplish?

A 30hp may barely plane the boat w/ one person, or it could make for the
perfect aluminum fish & ski boat with all the power you need for the
whole family(50 years ago a Scott 30/33 was a hot setup on a light
boat). A 100hp could be set up for 33mph top speed or 70mph top speed
with many variables determining the outcome.

Rob

[The Fuzz]

Ok then Rob. There is clearly a lot that I need to learn. And here it
begins.

So lets say 2 stroke engines on a 17ft Shakespeare hull. (So
fibreglass).

Average use, 2 adults on the Thames, so not much else in the boat.

Mission: pleasure and not sinking.

Would could I expect from that?

[Lost In Space/Woodchuck]

not knowing the hull design & weight I would guess mid 20mph with 100hp.

"The Fuzz" <Loudi...@breathe.com> wrote in message
news:1151224548.3...@b68g2000cwa.googlegroups.com...

[Wayne.B]

On Sun, 25 Jun 2006 07:39:26 -0400, "Lost In Space/Woodchuck"
<newsgro...@wildblue.net> wrote:

>not knowing the hull design & weight I would guess mid 20mph with 100hp.

100 hp is a lot of power on a 17 ft boat, probably 40 to 50 mph on
flat water, lightly loaded. With 50 hp it should be at least in the
mid 20s, maybe more.

50 hp is about the minimum for good performance.

[Eisboch]

"Wayne.B" <waynebatr...@hotmail.com> wrote in message
news:os3t921bn6qsiaqap...@4ax.com...

As a point of reference, a Boston Whaler 16' Dauntless with a 115 hp Merc.
(2 stroke) tops out at about 50 mph under ideal conditions.

Eisboch

www.eisboch.com

[Varis]

How does the material affect speed, besides the weight factor?
Rigidity, friction?

[trainfan1]

Varis wrote:
> How does the material affect speed, besides the weight factor?
> Rigidity, friction?
>

He gave us the material, because he doesn't know the weight.

Rob

[The Fuzz]

The kind of answer I am after here is what I've got a sniff of:

>As a point of reference, a Boston Whaler 16' Dauntless with a 115 hp Merc.
>(2 stroke) tops out at about 50 mph under ideal conditions.

Thank you Wayne and Eisboch.

I'm just trying to get a handle on what bang you get for you buck as
the engine sizes increase.

So what would I be looking at max ideal speeds for 2 stroke 50hp, 60hp
and 85hp?

And what do you get from a 4 stroke engine? Is it just better
acceleration and worse fuel ecconomy?

J

You catch my drift?

[trainfan1]

The Fuzz wrote:

OK...

6hp Johnson on 15' Alumacraft = 12 mph

115hp Evinrude(320lbs.), 19" P SS prop, on 750 lbs. 16' Glastron
Aqua-Lift Vee = 43 mph

220hp Ford V-8 inboard 16' Correct Craft 1750 lbs. total dry weight 12"
D x 14" P = 51mph on a good day

115hp Evinrude(320lbs.), 17" P SS prop, on 1100 lbs. 16' AeroCraft
Malibu Deep Vee = 39 mph

90hp Mariner 6 cyl.(~320lbs.), 23" P SS Quicksilver prop, on ~680 lbs.
17' Offshore DSC (Wahoo/Whaler Type) = 50.3 mph(radar)

That's all I've got going right now...

Rob

[The Fuzz]

Thats interesting.
So there is not *that* great an advantage between hp's then.

What about what you get from upping to a 4 stroke engine?

Now, regarding oil mixes. A neighbour of mine said that if I were to
use a 2 stroke motorcycle oil, instead of a marine specific oil, it
wouldn't be a problem because the engine is cooled by the water enough
and wont suffer.

How wrong can he be, if at all?

J

[The Fuzz]

Thats interesting.
So there is not *that* great an advantage between hp's then.

[trainfan1]

The Fuzz wrote:
> Thats interesting.
> So there is not *that* great an advantage between hp's then.

There are so many variables involved, even with one boat & motor
combination, the answer you want could be anything. The brand of motor,
for one, makes a difference. A 90 could be a V-4 OMC, 3 cylinder
in-line Merc, 6 cylinder in-line Merc/Mariner, 4 cylinder in-line
Suzuki, 3 cylinder in-line Yamaha. They all have different gearing,
bores/strokes, carburetion leading to widely varying powerbands & peak
HP & torque curves, and all this before you start to consider choosing a
prop - material, design, diameter, pitch, rake, blade area, number of
blades. I have 4 different props for each of the 16' boats, 3 for the
Offshore, just the one for the Johnson 6.

>
> What about what you get from upping to a 4 stroke engine?

Some would say moving to a 4 stroke is not "upping" depending again on
what you want to accomplish. They are heavier, have a lot more moving
parts and reciprocating mass, & generally higher acquisition cost. You
don't have to mix oil or buy 2 stroke oil, but you do have to do oil &
filter changes regularly. They are quieter at low speeds and do not
produce "2 stroke haze", but most are just as noisy at or near top
speeds. They don't foul plugs as easily as 2 stokes during extended idling.

>
> Now, regarding oil mixes. A neighbour of mine said that if I were to
> use a 2 stroke motorcycle oil, instead of a marine specific oil, it
> wouldn't be a problem because the engine is cooled by the water enough
> and wont suffer.
>
> How wrong can he be, if at all?

As long as the "motorcycle" oil is TCW-3 rated, it should be fine. Why
go out of your way, though, when TCW-3 outboard oil is so easy to find
(and often discounted)at any mass merchandiser, or a marina or ship's
store, & every convenience store & gas station.

Rob

[Varis]

trainfan1 wrote:

> Suzuki, 3 cylinder in-line Yamaha. They all have different gearing,
> bores/strokes, carburetion leading to widely varying powerbands & peak
> HP & torque curves, and all this before you start to consider choosing a
> prop - material, design, diameter, pitch, rake, blade area, number of
> blades.

So is there a nice source that gives a detailed overview of all those
parameters, or should you refer to different sources like outboard
books, boat design books, web sites etc?

Risto

[trainfan1]

Read, read, read.

Magazines & journals. Get a part time job at a marina.

Rob

[The Fuzz]

Thank you very much Rob and Gene.

That has me patched up with the basics I needed to know.
I'm very grateful to you.

>From a brief search of this group Risto, I'd say here is a very good
place to start to learn.
For starters, I found Prof Arthur Waites propeller info. Very good
stuff:

http://groups.google.com/group/rec.boats/browse_thread/thread/12b5e93cd1e7ea98/0d6c3ed7191f26eb?q=propellers&rnum=4#0d6c3ed7191f26eb

One thing Rob said that intrigued me though.

4 props per boat?

What are you up to out there?

[trainfan1]

The Fuzz wrote:
> Thank you very much Rob and Gene.
>

> One thing Rob said that intrigued me though.

>
> 4 props per boat?
>
> What are you up to out there?
>

Outboard Glastron example:

1)19" SS & 2)19" Cupped Alum - Lighter loads(the normal prop for this
boat) and a backup

3)17" SS for long days w/ full loads & tubing, 4)17" Alum backup

5)15" large surface area aluminum for demonstration skiing(up to 5
skiers on this boat). Engine overspeeds with this prop, so you need to
be careful once the skiers are up.

Oops, I guess that's 5...

Rob

[justa me]

A 90hp Yamaha 2stroke 3cylinder on a 17ft Cabin Boat with total mass of around 840kg on the water :

Speed ?

[gfre...@aol.com]

I am guessing mid 30s. A lot would depend on hull design.

[mgmi...@gmail.com]

16’ Wahoo with a 90hp Suzuki 4 stroke and 23” SS Prop?

[gfre...@aol.com]

On Sun, 31 May 2020 15:03:51 -0700 (PDT), mgmi...@gmail.com wrote:

>16’ Wahoo with a 90hp Suzuki 4 stroke and 23” SS Prop?

~45 ?

[Bill]

23” per revolution, 4000 rpm, doesn’t that work out to a little over a 1000
mph? ;)

[gfre...@aol.com]

Actually a little over 50 MPH at 6000 RPM
(minus the slip)
DF90A WOT RPM should be 5300-6300 with a 2.59 gear reduction.

When you do the math you end up around 50.
10% slip gets you 45.