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01-17-2021, 12:15 PM #16000 RPM
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Outboard Motor Test Tanks: Design & Construction
I’ve been a member here for a long time and have seen almost every conceivable topic come up in the Tech forum. One that I don’t remember even being covered in detail is outboard motor test tanks. Instigator did a thread on test pits (which are similar), and Jay Smith once had a thread on an engine run stand, but I wanted to dig into fabricated water test tanks in-depth (pun intended).
My goal is to build a multi-functional heavy duty test tank. I’ve been researching it for awhile now, and will gradually post key design considerations that have come up. Constructive input from other members, especially professional OB technicians, would be very helpful. I figured that other DIY-ers might also be thinking about building one, hence posting this thread to put it all in one place.
Some of you must be thinking by now: what the hell is so complicated – it’s a glorified rain barrel right ?!
Ha, ha, yes – and no. When you start to dig into this there’s actually a lot to consider. If you Google OB test tanks you’ll find lots of YouTube clips of people running small motors in garbage cans, old chemical totes with the lid cut open, 55 gallon drums, et cetera. That’s not where I’m at. The goals for me are:
- Tank large and strong enough to run a 300+ hp OMC at WOT with a test wheel/prop
- Modular so it can be disassembled and stored reasonably easily (I have never seen a tank like this)
- Multi-functional so it can be used in three applications:
- Larger motors mounted on an engine stand that gets wheeled up to the tank, then locked together (for use with test propellers). This design is commercially available, but only for smaller motors.
- Smaller motors (say up to 30hp) that get clamped to a transom plate directly on the tank (i.e. typical of traditional test tanks)
- Able to be setup to test an engine that is already mounted on a boat (i.e. “wheel-up” or “drive-up” tanks, which are also commercially available).
- Reasonably priced. I will 100% admit I’m kinda cheap lol. I’m sure I could pay to have this built, but that is not going to happen.
The next post will be looking at the Pros and Cons of commercially available tanks from manufacturers like Kerr Tool and Specialty Motors.
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Instigator liked this post
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01-18-2021, 04:11 AM #2
Easily disassembled no
Easily stored yes as it is on wheels
Cheap!? Build it myself fits 30 inch engines
Running a big engine gives a lot of fumes
I use the paint fume exhaust fan for this
If you dyno for prolonged times the water heats up so i installed an overflow which feed into the bottom
Heated water should have a lower density and migrate to the surface where it overflowes into a drain
I am available for engineering advice if you pay for my airplane ticket!
Always wanted to see Canada 🍁 😇
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MattGreen thanked for this post
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01-18-2021, 08:16 AM #3
I’m still pondering my pit idea and want to start digging.
My hurdle is what to use on the dirt walls to keep them from collapsing from water saturation and erosion from 300 hp at WFO.
Figured a cheap way would be plywood, skinned w/rubber roofing.
Back side of plywood would likely last s few yrs before rotting.
Matt, I’ve thought of the test tank idea too but 300 hp’s, @ WFO w/a test wheel?????
Ur gonna need a bigger tank.
Look at plastic, bellow ground septic tanks.
All the big box stores have them and have my attention.
Big ones are probably 1000 gals??
Could notch one end, allowing a tilted motor to be backed in, bolt on a motor board for small motors and mount it to a wheeled cart.
??????Last edited by Instigator; 01-18-2021 at 08:18 AM.
I'd rather be competitive w/junk I built in my garage than win w/stuff I bought.
I refuse to allow common sense to interfere w/my boat buying decisions.
Checkmate 16' 140 Johnson
Hydrostream 17' Vector FrankenRude I
Laser 480 (?) 21' w/GT 200
Glastron Carlson Conquest w/XP 2.6
Glastron Carlson CVX 20 w/XP 2.6
24' Sonic w/twin 250 Johnsons
24' Sonic w/twin 250 HO Johnsons
19' STV River Rocket w/FrankenRude II
Allison XR 2002 w/Frankenrude II
Hydrostream 18' V-King w/Frankenrude II
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MattGreen liked this post
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01-18-2021, 08:43 AM #4
These are a couple I tried to sell several years ago. The aluminum tank was mainly for jet skis and had a boom for lifting them and a circulating pump along with provisions for a vacuum. There were chains to hold ski in place. The steel tank was for boats and also had a circulating pump and a vacuum for fumes. The steel tank was in ground with hydraulics to lift it to boat. Could not find a home for either so aluminum tank was cut into pieces and steel tank was filled with scrap and taken to scrap yard. It sucked to kill them both but as you can see they are fairly large and took up a lot of space. Hopefully you can get some ideas from these pics.
RockTeam Junk
No sparkling wiggles in here, only dump truck grinches.
"Screamin Heathen"
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Instigator, MattGreen thanked for this postInstigator, tnelsmn liked this post
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01-18-2021, 08:49 AM #5I'd rather be competitive w/junk I built in my garage than win w/stuff I bought.
I refuse to allow common sense to interfere w/my boat buying decisions.
Checkmate 16' 140 Johnson
Hydrostream 17' Vector FrankenRude I
Laser 480 (?) 21' w/GT 200
Glastron Carlson Conquest w/XP 2.6
Glastron Carlson CVX 20 w/XP 2.6
24' Sonic w/twin 250 Johnsons
24' Sonic w/twin 250 HO Johnsons
19' STV River Rocket w/FrankenRude II
Allison XR 2002 w/Frankenrude II
Hydrostream 18' V-King w/Frankenrude II
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MattGreen thanked for this post
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01-18-2021, 09:20 AM #6Screaming And Flying!
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I built one for a marina from 1/2'' ply and mat glass over it. Don't remember the x-act dims but it had a partial hinged cover to keep the water in it for the most part. Seems 3'deep x 6 'long x 4' wide. Back boat up to it trim motor down into it. They adj boat with forklift for up and down. Lil motors just clamped on to the front edge which was doubled up wood for strength.
83 V-King, 96 Mariner, 200 hp ff block 2.5 w/a 28p choppa
We gotta clean this liberal mess up, VOTE TRUMP TO MAGA!
Rebuild thread:
http://www.screamandfly.com/showthre...-it&highlight=
http://www.screamandfly.com/showthre...cs.&highlight=
Videos
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MattGreen thanked for this post
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01-18-2021, 09:24 AM #76000 RPM
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Thanks guys, this is exactly the type of brain-storming I was hoping to initiate. Tank volume is a key consideration - large enough to run the big engines and reasonable “heat sink” capacity, but balanced with the physical footprint of the tank.
Exhaust ventilation is of course another. That will be a focus area that I’ll dig into in a fair amount of detail. Two strokes produce lots of carbon monoxide (CO) so even if used outside that needs to be considered.
More to come,
Matt
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01-18-2021, 07:47 PM #8
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Instigator liked this post
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01-18-2021, 08:39 PM #9
Double R Has an in ground, it has wash tubes that returns the water back to in front of the props.
2023 TUFF 25
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Instigator thanked for this postInstigator liked this post
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01-19-2021, 08:20 AM #10I'd rather be competitive w/junk I built in my garage than win w/stuff I bought.
I refuse to allow common sense to interfere w/my boat buying decisions.
Checkmate 16' 140 Johnson
Hydrostream 17' Vector FrankenRude I
Laser 480 (?) 21' w/GT 200
Glastron Carlson Conquest w/XP 2.6
Glastron Carlson CVX 20 w/XP 2.6
24' Sonic w/twin 250 Johnsons
24' Sonic w/twin 250 HO Johnsons
19' STV River Rocket w/FrankenRude II
Allison XR 2002 w/Frankenrude II
Hydrostream 18' V-King w/Frankenrude II
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01-19-2021, 08:28 AM #11
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Instigator liked this post
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01-19-2021, 09:14 AM #12Screaming And Flying!
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Every guys dream home right there. Just missing the girls in bikinis.
83 V-King, 96 Mariner, 200 hp ff block 2.5 w/a 28p choppa
We gotta clean this liberal mess up, VOTE TRUMP TO MAGA!
Rebuild thread:
http://www.screamandfly.com/showthre...-it&highlight=
http://www.screamandfly.com/showthre...cs.&highlight=
Videos
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01-19-2021, 09:20 AM #135000 RPM
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Instigator thanked for this postInstigator liked this post
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01-19-2021, 09:40 AM #146000 RPM
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Xstream you confirmed the rough dimensions I had in mind. My plan at this point is to build it from fiberglass cored with 1/2" Nidacore, which is actually cheaper in my area than marine plywood. I was going to build a plug with generously-radiused corners to make it less "boxy" than metal fabricated tanks. Some of the materials are leftover from other projects, I'm trying not to lay out too much dough on this. Do you think skins of 1x 18 oz roving plus 1x 1708, finish with 0.75 oz CSM (same skin in & out) would be about right ? Strength in all directions plus this is what I have lying around.
Flabum, I knew somebody was going to toss that out there - lol - I'm jealous ! If I had good access to a boat ramp there would be a lot less need to build this tank. Where I currently live the boating season is roughly 3 months long, and the closest ramp where I could do engine work with a test wheel is an hour's drive away. I want to be able to test/break-in/setup jetting on engines in the dead of winter (I have a heated shop) so I'm good to go for when summer eventually arrives.
RBT, thanks for that info, I was not aware they had a big tank like that. I had thought of using PVC pipes within the tank for that purpose. For everybody's benefit, what Rob is getting at is if you run engines with props attached, you push much of the water to the back of the tank (riding up the back wall like a big wave), and the prop starts to suck air. This can get into a bad rhythmic cycle that alternately loads and unloads the engine - unstable operation - not good for anything. I've seen this in test tanks running with props on, especially if the water level is a bit low. This is one of the reasons that OB manufacturers produce test wheels/props that make negligible thrust. My understanding so far is that there are three strategies to minimize this issue (if you run props): baffles for smaller tanks; wash tubes for larger tanks; round tanks that will tend to naturally circulate the water back to the props; or some combination of these. This issue overall is one of the design considerations that makes test tanks more complex than just a box. I have test props for V4 engines and up, and would rarely need to test anything in the 30-70 hp range. The only engines I'm likely to run in my tank with props would be 30 hp and below which I have seen successfully managed with baffles.
Test props are not without their own issues, they sort of just re-direct the problem. You MUST have a tight-fitting lid on a tank running a test prop on larger engines or you will just throw the water out of the tank. The lid can then impede exhaust ventilation - I'm working on that issue too. I'm planning to actually have two sets of baffles - at the back for prop-wash, and at the sides to re-direct water thrown from test props.
Keep 'er coming folks, good stuff here
Matt
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01-19-2021, 09:45 AM #15
Test wheels have an issue that most forget, they create no forward thrust that the design of the case/bearings need
2023 TUFF 25
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