Outboard vs Inboard with same hp on similar hull

Designs for inboard or outboard power

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scottp
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Outboard vs Inboard with same hp on similar hull

Postby scottp » Thu Jun 29, 2017 4:44 pm

Just based on cost and ease of maintenance etc I am looking at the 35 hp power range as the
largest of the new V-twin aircooled engines as run in commercial riding mowers.

I have zero experience building boats or boat drivetrains but from reading as much as I can about
the Glen-L Tiny-Might and their listed requirements for an inboard drivetrain, it would appear that
$2000 should cover everything non engine related with a Briggs Vanguard V-Twin or a Kohler V-twin
being about $2500 for a mechanical grand total of $4500. I believe the whole mechanical setup
would weigh about 200 or 225 pounds. So compare that to the cost of a 35 hp 4-stroke outboard
in cost and weight and for me the inboard would have all the advantages.

For those familiar with inboard operation, am I missing anything here ? Am I correct to assume
similar performance ? What wears out after a few hundred or a thousand hours in an inboard setup
and needs costly replacement that would be a disadvantage compared to outboards ?

Video of 20hp air cooled engines in operation....


Two VIDEOs
https://www.youtube.com/watch?v=3SLStzb ... nnel=KarlN

https://www.youtube.com/watch?v=Nj7jSxi ... nnel=KarlN

DSR
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Re: Outboard vs Inboard with same hp on similar hull

Postby DSR » Fri Jun 30, 2017 10:07 pm

Hi Scott

I was intrigued by the idea of using the B&S Vanguard 35hp V-twin in the Tiny Might and I don't think there would be any issues mechanically adapting it for a direct drive application.
I would definitely investigate a couple of items that I see immediately that may become issues though -

With the Vanguard being an air-cooled configuration (looks like a semi-ducted fan cooling setup by the pictures I've looked at),I would be concerned regarding issues with providing adequate engine cooling under an enclosed engine hatch such as what the Tiny Might is shown with (even omitting the hatch and leaving the engine area open may not provide enough airflow but i'm not positive on that....)
I would have similar concerns regarding controlling exhaust heat also.....
And with engine not having appropriate marine-specific ignition and fuel systems with their related safeguards, I'd be hesitant to running the engine in even a semi-enclosed engine compartment
I myself do not see these issues as a deal-breaker by any means, just as items that would need to be investigated and addressed as necessary and with the lighter powertrain weight and the bullet-proof simplicity, it would make for a really fun little package (not a speed demon but it'd be a lot of fun in a cost-effective package...), I like it!! :D

Thanks Scott
Dave
DSR Performance - Home of yet another jet TNT build :D
Codename "Just A Little....."
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sproggy
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Re: Outboard vs Inboard with same hp on similar hull

Postby sproggy » Sat Jul 01, 2017 12:55 am

The Vanguard appears to rev to only 3,600rpm which is a pretty limited rev range - diesels rev higher than that! There's an option of a "High Speed 4750rpm Package", though. A whole 4,750.... I'd worry about airflow as stated above.

I would have thought a better donor would be a jetski - an old 550 would give enough power and be cheap as chips to buy. The motor would be water-cooled with a water-cooled exhaust and no doubt smaller and lighter than the B&S motor. No concerns about getting adequate airflow either. I'm not suggesting using a jet - just use the motor and gear it so suit a prop or, if no gearbox is required, fit a small-pitch prop that suits the engine's rev range.

Bear in mind that hull designs intended for outboards have more hull volume aft to support the weight of the motor on the transom. So mounting an inboard further forward would adversely affect weight distribution. On something of the size you're talking about you could probably offset this by putting the battery and fuel tank aft, right near the transom.

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chugalug
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Re: Outboard vs Inboard with same hp on similar hull

Postby chugalug » Sat Jul 01, 2017 6:47 am

I've always wondered about a liquid cooled snowmoble engine using a clutch setup somehow.
Working on regular-sized Bo-Jest


"If it's not crooked,It's not mine

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sproggy
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Re: Outboard vs Inboard with same hp on similar hull

Postby sproggy » Sat Jul 01, 2017 9:42 am

chugalug wrote:I've always wondered about a liquid cooled snowmoble engine using a clutch setup somehow.


I don't have any knowledge of snowmobiles but I'd imagine they must have some sort of clutch fitted to allow them to idle without moving? Do they have reverse gear?

You'd still have the challenge of cooling the exhaust and they might not cope well with with raw water cooling, particularly in salt water.

Given that people like Polaris/Bombardier make both PWCs and snowmobiles I'd guess there's a fair amount in common between some engine designs in both. But the exhaust arrangement would make the PWC version a better bet (PWC = Personal Watercraft this side of the Atlantic - not sure whether you use the same term?).

Probably the ideal combination would be a PWC motor with a snowmbobile (equivalent engine) gearbox. Maybe I'm making assumptions about their similarity that aren't valid, though.

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Bill Edmundson
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Re: Outboard vs Inboard with same hp on similar hull

Postby Bill Edmundson » Sat Jul 01, 2017 10:10 am

When converting engine to marine, The starter, alternator, and anything that might generate a spark must be sealed so they can't set off gas fumes.

Bill
Mini -Tug, KH Tahoe 19 & Bartender 24 - There can be no miracle recoveries without first screwing up.
Tahoe 19 Build

DSR
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Re: Outboard vs Inboard with same hp on similar hull

Postby DSR » Sat Jul 01, 2017 10:38 am

A little bit of creative brainstorming, gotta love it!! It just seems to go hand-in-hand with boatbuilding. :D

A properly sized PWC engine would be a great fit for the Tiny Might and like Sproggy said, already marinized. That was my choice for the TNT that I'm getting ready to build (but I am using the whole powertrain in a jet conversion). The only issue there would be to add a water pump for cooling as PWCs use water pressure bled off of the jet pump to cool. A remote-mounted electric water pump possibly? There are 12V remote-mounted pumps available
Also no gearbox......
A liquid-cooled snowmobile engine is a great possibility that I've not thought of and quite a few do have reverse (I believe that the gearbox / reverse units are integrated into the engine design itself and not a separate unit). Fabricating a water-cooled exhaust is entirely feasible. Possible issues with non-marine ignition and fuel systems would still need to be addressed......

......A devious mind is a terrible thing to waste...... :lol:
DSR Performance - Home of yet another jet TNT build :D
Codename "Just A Little....."
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Hercdrvr
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Re: Outboard vs Inboard with same hp on similar hull

Postby Hercdrvr » Sat Jul 01, 2017 11:13 am

Mr. Witt cautioned against using air cooled non marine engines in boats. He said they were not designed for the demanding loads of marine use and a hot air cooled engine in a boat is unsafe.
So proceed at your own risk and have fun.

Matt B

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Mr Hot Rod
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Re: Outboard vs Inboard with same hp on similar hull

Postby Mr Hot Rod » Sat Jul 01, 2017 11:57 am

More info about snowmobile chaincases modified to build a chain driven v-drive or z-drive :


The newer engines have electronic reverse (push-button actuated) and don't need a mechanical reverse chaincase.

A PWC engine would be preferred because of the watercooled exhaust and USCG approval.

____________________
Paul Kane
Kane Custom Boats Ltd.
Chelsea, Quebec

Building the Glen-L Hot Rod : http://www.kanecustomboats.com
Glen-L Hot Rod build thread
Kane Custom Boats YouTube channel
Glen-L Boat Video Directory

DSR
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Re: Outboard vs Inboard with same hp on similar hull

Postby DSR » Sat Jul 01, 2017 12:45 pm

It never fails to surprise me how much information is available here on the forum!

Thanks Paul!! :D
DSR Performance - Home of yet another jet TNT build :D
Codename "Just A Little....."
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Denon Osterman
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Re: Outboard vs Inboard with same hp on similar hull

Postby Denon Osterman » Tue Jul 18, 2017 7:30 pm

As a proud Canadian (who's late to the game on this thread, admittedly), I know wayyy too much about snowmobiles. I'd say the PWC route is much better for a few reasons. Keep in mind everything I say is only relevant to older 2 stroke engines, but those are the cheap and easy ones you'd likely be looking at anyways.

1) Exhaust. Sled (snowmobile=sled) engines like big, *hot* exhaust. It is not water cooled and their timing curves are not designed for it to be anything other than water jacketed. You'd definitely want water jacketed exhaust and at that point you've likely found the engine it came with anyways!

2) Transmission. I've never seen a snowmobile that *didn't* use a belt driven CVT. These work great for the torque and power applications a snowmobile requires - but would be very unsuited to a boat. They are somewhat integral to the engine, in the sense that the primary clutch rides directly on the drive shaft. And, they're a consumable item - you ALWAYS ride with a spare belt, and need to have a CVT tool to change it for when it inevitably blows. If you ride often and hard, that's more than once a season.

3) Power and tuning. Similar to above, sled engines and PWC engines - even if they have the same block - are not tuned the same. A PWC needs torque relatively evenly distributed, generally only revs to ~6-7k rpm, and has a much more usable power band. Sleds are meant to be pinned to the bar, rev 8-9k, and jump on the torque rather suddenly. The CVT is meant to do all of the work for keeping the power band there, so the engines are meant to peak their torque right at redline and only really there. Side note - the pull you get on a well tuned engine in a snowmobile is *phenomenal*, much better than even a jetski once you've started moving. The *instant* response might not be quite there, but because it starts off kinda slow, then finally hits redline, then the CVT starts climbing, then the track stops slipping...you find yourself doing 100 mph faster than you can say "this is way too fast" :wink:

4) Durability. Not nearly as big of an expert on a PWC engine, but given snowmobiles are pushed to the limit, they require pretty regular and intensive maintenance. Re doing an entire top end, "blowing" an engine, cleaning the carbs, are all part of the fun. On that note, electric starting - at least for older, cheaper engines - is extremely rare! Sled's are all about lightweight, so gears meant to handle torque, electric start, reverse (the old "gearbox" reverse is equally rare) are all difficult to track down.

In short, a sled engine is meant to be as fast and lightweight as possible, whereas a PWC engine is meant to be safe, reliable, hassle free, etc. I might love sleds even more than I love boats - pics attached for anyone who shares a love - but I'd never try stuffing a skidoo engine in a boat!

IMG_20161130_203258.jpg


IMG_20161130_203201.jpg


DSC_1447 - Copy.JPG


Just my $0.02

Denon


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