The Right Size Outboard Gas Engine for a 18-ft Boat?
 

I would like to know the proper size outboard gas engine that I should
put on a 18-ft aluminum semi-V/deep-V boat.

According to Tracker web site, they stated that the max HP for their
16-ft deep-V aluminum boat is 40HP. I would assume that the max HP of a
similar 18-ft boat "may" be around 50HP (?)

Obviously, this 50HP figure is just the maximum limit. And I may want
something smaller than 50HP to save gas, to reduce noise, to reduce
weight that an electric motor has to pull. But if I go to the other
extreme by getting a very small engine, I may spend too much time
"getting there" especially against the current. Somewhere between the
maximum and the minimum, there may be a horsepower rating that is
appropriate for my need.

Let explain what my needs a
- Put the gas engine in a 18-ft alumimum boat.
- Carry 4 adult males (let's say 750-lb total).
- Use it strictly for fishing, not for skiing.
- I like to drive my car at or below speed limit,
not over it. Likewise, I operate a boat at
moderate speed only.
- Want a quiet engine (I guess I need a 4-stroke
engine).
- Want to save gas money.

What size gas engine should I get? A range of horsepower should be
fine.

Thanks for any info in advance.

Jay Chan

wrote:
I would like to know the proper size outboard gas engine that I should
put on a 18-ft aluminum semi-V/deep-V boat.

According to Tracker web site, they stated that the max HP for their
16-ft deep-V aluminum boat is 40HP. I would assume that the max HP of a
similar 18-ft boat "may" be around 50HP (?)

Obviously, this 50HP figure is just the maximum limit. And I may want
something smaller than 50HP to save gas, to reduce noise, to reduce
weight that an electric motor has to pull. But if I go to the other
extreme by getting a very small engine, I may spend too much time
"getting there" especially against the current. Somewhere between the
maximum and the minimum, there may be a horsepower rating that is
appropriate for my need.

Let explain what my needs a
- Put the gas engine in a 18-ft alumimum boat.
- Carry 4 adult males (let's say 750-lb total).
- Use it strictly for fishing, not for skiing.
- I like to drive my car at or below speed limit,
not over it. Likewise, I operate a boat at
moderate speed only.
- Want a quiet engine (I guess I need a 4-stroke
engine).
- Want to save gas money.

What size gas engine should I get? A range of horsepower should be
fine.

Thanks for any info in advance.

Jay Chan



There should be a plate on the boat giving the maximum horsepower for
that hull and the maximum number of people or weight allowed.

-Raf

--
Misifus-
Rafael Seibert

http://www.ralphandsue.com

"Misifus" wrote in message
news:yChWe.20499$dm.12431@lakeread03...
wrote:
I would like to know the proper size outboard gas engine that I should
put on a 18-ft aluminum semi-V/deep-V boat.

According to Tracker web site, they stated that the max HP for their
16-ft deep-V aluminum boat is 40HP. I would assume that the max HP of a
similar 18-ft boat "may" be around 50HP (?)

Obviously, this 50HP figure is just the maximum limit. And I may want
something smaller than 50HP to save gas, to reduce noise, to reduce
weight that an electric motor has to pull. But if I go to the other
extreme by getting a very small engine, I may spend too much time
"getting there" especially against the current. Somewhere between the
maximum and the minimum, there may be a horsepower rating that is
appropriate for my need.

Let explain what my needs a
- Put the gas engine in a 18-ft alumimum boat.
- Carry 4 adult males (let's say 750-lb total).
- Use it strictly for fishing, not for skiing.
- I like to drive my car at or below speed limit,
not over it. Likewise, I operate a boat at
moderate speed only.
- Want a quiet engine (I guess I need a 4-stroke
engine).
- Want to save gas money.

What size gas engine should I get? A range of horsepower should be
fine.

Thanks for any info in advance.

Jay Chan



There should be a plate on the boat giving the maximum horsepower for that
hull and the maximum number of people or weight allowed.

-Raf

--
Misifus-
Rafael Seibert

http://www.ralphandsue.com

Bigger engine may not use more gas. Unless you run it wide open. The
smaller engines can use more fuel, as they have to be run in the upper range
of the throttle to get the performance required.

Generally, less than 20 percent of the rated max hp will significantly
degrade performance.
As for the difference in noise between a 40 and 50 hp engine, it's
insignificant. Besides current engines are much quieter than previous
two-strokes.
ed
marine engine digest

On Thu, 15 Sep 2005 12:47:50 -0700, barry wrote:

wrote:
: I would like to know the proper size outboard gas engine that I should
: put on a 18-ft aluminum semi-V/deep-V boat.

: According to Tracker web site, they stated that the max HP for their
: 16-ft deep-V aluminum boat is 40HP. I would assume that the max HP of a
: similar 18-ft boat "may" be around 50HP (?)

50 HP seems very low for an 18 Ft. boat. I'd think something closer to 75 to
100 HP would be more reasonable.


An 18-ft Aluminum is a LONG way from a Bayliner! And some engines (not car
engines, but inboard diesels and I THINK outboards) are MOST efficient at
or near WOT.

40-50hp sounds fine for his boat and his needs. I'd say go 4-stroke for
quietness, although you might want to check the specs of your boat to see
if there's an engine weight restriction.

And considering your other post about taking it on and off, you MIGHT get
by with a 25hp 2-stroke, depending on how slow you're willing to go.

Lloyd Sumpter
"The Tin Boat" Mirrocraft 12

Generally, less than 20 percent of the rated max hp will significantly
degrade performance.

I assume you mean an outboard engine will reduce its performance
significantly if we operate it below 80% of its max hoursepower rating.
Do I understand this correctly?

In other words, I need to run an outboard engine at or near its peak
horsepower rating. This also means that I need to buy an outboard
engine whose _max_ horsepower rating matches the cruising speed of the
18-ft boat that I intend to operate at.

I probably want to cruise at a leisure speed of 10 to 15-miles-per-hour
(here the miles are not nautical miles). What kind of horsepower an
outboard engine should have in order to push a 18-ft boat with 4 adults
males on it at the cruising speed of 10 to 15 miles-per-hour? Any idea?
Thanks. I appreciate your help.

As for the difference in noise between a 40 and 50 hp engine, it's
insignificant. Besides current engines are much quieter than previous
two-strokes.

Good to know this. This means I should concentrate on getting the
proper horsepower to push the boat instead of being distracted by other
factors.

Jay Chan

... And some engines (not car engines, but inboard diesels
and I THINK outboards) are MOST efficient at or near WOT.

I assume WOT means "wide open throttle". This means I need to get an
outboard engine that will run at or near its rated max horsepower when
it can push the 18-ft boat at the cruising speed that I intend to
operate the boat at. (The speed that I intend to run the 18-ft boat is
like 10 to 15 land-miles per hour). This sounds good to me because this
means I can buy a low cost small engine and run it near top speed
instead of buying an expensive big engine and run it at low speed. This
works out great for my money. Thanks for the good news.

40-50hp sounds fine for his boat and his needs. I'd say go 4-stroke for
quietness, although you might want to check the specs of your boat to see
if there's an engine weight restriction.

Thanks for confirming that 4-stroke engine is quieter than 2-stroke.

I am not sure if I really need a 40-50hp engine because my intended
cruising speed is only 10 to 15 land-miles-per-hour. Actually, I don't
know because I really don't know how small an engine can push the 18-ft
boat at 10 to 15 miles-per-hour cruising speed.

And considering your other post about taking it on and off, you MIGHT get
by with a 25hp 2-stroke, depending on how slow you're willing to go.

Actually, I am thinking of 9.8hp because many lakes in New Jersey
(where I live) have restriction to limit the engine to no more than
10-hp. And a 9.8hp 4-stroke engine is around 90-lb; two persons with a
carrier should be able to hoist it. I am currently leaning toward
getting a 9.8hp as long as it can push the 18-ft boat with 4 adult
males on it at 10 to 15 land-miles per hour. What do you think?

Thanks for any info in advance.

Jay Chan

Actually, I am thinking of 9.8hp because many lakes in New Jersey
(where I live) have restriction to limit the engine to no more than
10-hp. And a 9.8hp 4-stroke engine is around 90-lb; two persons with a
carrier should be able to hoist it. I am currently leaning toward
getting a 9.8hp as long as it can push the 18-ft boat with 4 adult
males on it at 10 to 15 land-miles per hour. What do you think?

You are going to need at least a 15 to do what you intend to do, but I
believe that a 25 is going to be much more appropriate.

This is kind of disapponting to know this; I am hoping that a 9.8hp
will be good enough. Seem like I will need a 25hp outboard gas engine.
In this case, I need to get a very powerful electric trolling motor for
lakes that are electric only or limit to 10hp-or-less. Luckily, those
lakes that have restriction tend to be small lakes (with some
exceptions).

Oh well...

Thanks anyway.

Jay Chan

On 16 Sep 2005 09:08:28 -0700, wrote:

SNIP

Actually, I am thinking of 9.8hp because many lakes in New Jersey
(where I live) have restriction to limit the engine to no more than
10-hp. And a 9.8hp 4-stroke engine is around 90-lb; two persons with a
carrier should be able to hoist it. I am currently leaning toward
getting a 9.8hp as long as it can push the 18-ft boat with 4 adult
males on it at 10 to 15 land-miles per hour. What do you think?

Thanks for any info in advance.

Jay Chan

Boy I hope you don't ever intend to go into rivers and that the lakes
have no current. A 9.8 with that load might not even hold its own in a
stiff current. I remember watching my brother in a 15ft aluminum boat
with an older 25 Hp on it sitting in the Little Kanawa river near
Parkersburg, WV. The river was high and flowing fast, but not yet at
flood stage. He was sitting still with the engine WOT. Could not make
any headway at all and barely got it back to shore where we could tie
it back up to the dock. At normal current it would do OK and get on
plane with him in it. I couldn't see it doing much with 4 full sized
men in it though.

The Other Dave hall
Dave Hall

"The power of accurate observation is commonly called cynicism by those who
have not got it." -- G.B. Shaw