Gulf Coast Crustacean Research - Boating Fuel economy
OK, recently Paul from the marina has hooked me up with a tweaked up Boston Whaler That got me to thinking about boats and fuel economy.
Now we all cringe when we go to the pumps but there are several ways to get it down to nothing more than a nervous tic.
A couple of months back I was playing with an over powered Bass boat.... Basically it was nothing more than a fiberglass slab of foam with A glassed in gas tank, a center console stand w/battery box a seat on a short pole up front, a small seat behiind the console with a glassed in leg pocket area and a couple of glassed in livewells. On it was a Merc Black max pushing 190hp through a prop that would be at home on a 250 no prob. This little puppy moved. Boat was light, unsinkable, not highly likely to break up and cut the water well enough that it would hit the mid 90's before the bow started feathering out (boat was only 18ft long, 5 wide and about 16 inches thick at the thickest point aft) and my redneck ass just did not have the guts to give it more gas (too easy to flip).
Now after you have knocked yourself in the head for taking so long to realise why my roommate will not get on a boat with me......
Consider this:
That boat was running at about 1/2 throttle on an engine that had only lightly been modified. We had a black max 150 with the carbs from a 175, had a macine shop polish the reed blocks, replaced the coil packs with accel Yellow Super Coils and swapped out the props till we had the fastest one.
at 80-85mph we were sucking down 2.8 gallons of gas per hour Now taking the lower number of 80 we get 28.571 miles per gallon - about on par with your car and probably better than your truck Drop the speed down to 50 and it drops to 1.2 gallons per hour or 41.6 miles per gallon or about the upper levels of the average small car mileage.
So we come to the Boston Whaler I am using for back and forth to the marina. 13ft long with a tweaked on little Yamaha 40 horse pulling 1.6 gallons per hour at 50 miles an hour Still excellent mileage and it is a very stable, unsinkable craft Ideally suited for its purpose.
So what does this mean to your boat? Well, I am getting to that.
Little things like keeping it tuned are nice but a good set of high voltage coils and 1 heat range lower plugs can improve your mileage up to 20 percent or so. Mods like this rarely affect your warranty.
Little tweaks like a polished reed block, properly tuned exhaust (yup there are still marinas out there that will tune an exhaust) Niether the machine shop polishing your reed blocks nor the marina tuning your exhaust is going to be cheap but when you are talking about permanent gains of 10-15% better fuel economy it is the far cheaper alternative. Granted this is something you do not want to do to the engine that is still under any kind of a warranty that says it will void your warranty.
Re-prop it 100% this is the best thing you can do for your engine. Most marinas will co-operate but be prepared to lay out some cash to play this game. Here is how it goes - you need to actually try a few props on your actual boat. Use the guides out there as guidelines in selecting what you want to try and find a marina that will sell you a few used props on the "I am gonna bring these back" understanding - be up front with them tell them exactly what you are doing and you know you are stuck with the prop hub bushings/adapters that are going to be needed to really try them out. Sounds expensive but you would be amazed at how many people are running a prop right for their boat if it was block stock and did not hgo out in more than Ideal conditions. You need enough prop to keep your engine from over-revving and at the same time you want little enough prop that it is not having to strain its every bolt to pull it. An overloaded engine is really inefficient. Find the speed range you usually run in, top off, run it, check your rate of consumption vs speed and go with the prop that gives you the best economy. Same rule applies to boats that are pulling or pushing loads - try a few props out with whatever type of load you usually pull or push. Go with the one that costs you the least at the pump yet gets the task accomplished in a manner that is acceptable to you. Marinas will do this for you but be prepared to spend 1500 bucks or more for them to take the kind of time to do theses tests for you. Most of the time they are happy you are willing to try a few yourself - and be nice - the marina that lets you return all those un needed props DESERVES your business for the prop you decide is best for your boat - and if the one you were trying was a used one - dont try to talk them down on the price - they did you a big time favor and it is only right to return the favor.
Other little things you can do are make sure you have enough engine for the boat. Take a 24ft Scout Bay. with a 150 you are pulling 5-6mpg while the 250 at the same speed gives the boat a sweet spot around 45mph at just touching 10mpg -14 after tweaking the engine a bit.
Now if you are purchasing a new small boat or have one that you are wanting to re-power..... consider smaller twins.
Some examples are:
My old 22.5ft Aquasport Pro-Line with a Carolina Cutter/Flatback style hull. Only mods to the hull were that the built in 180 gallon 2 tank setup was added as a replacement to the factory 90 gallon single tank. Entire hull was re-glassed over 3/4" home depot styrofoam in all the inner cavities including the top of the interior of the Cuddy. Exterior was very sun-faded Factory paint. Transom was re-inforced along the way with 3/4"x4" angle Aluminium I generally pulled her out every 2 or 3 months and hit the bottom paint ONLY with regular out of the bottle turtle wax which gained me speed across the board regardless of which engine I used. (like in the 7/tenths of a mph range)
Call that boat an engine slut but for a while there she saw quite a few and it was more my fault than hers.
Honda 235 with a Solas Prop 8.3 gallons per hour @ 63mph
7.7 gallons per hour @ 50mph
Engine was unreliable and replaced with a 300 Merc Black Max tweaked to about 450HP pushing hand picked props,tested about 20 sets before keeping that combo from 2 different manufacturers.
Merc Black Max 300 as described 10.3 gallons per hour @ 85mph
Engine was sold on second run to a passenger who just plain wanted it.
Johnson 155 Commercial - 7.2 gallons per hour @45 Mph
Engine came with the boat, had bad head gaskets, faulty temp indicator (did not go off) and a bad impeller.
Twin Johnson 70's 5.1 gallons per hour @ 38mph
4.2 gallons per hour @ 30mph
Temporary engines put back on the boat they were borrowed from.
Ernie Special 90 - lower unit from a 90, center section and exhaust chamber from a 115, powerhead from a 125, carbs from a 175 (just 2 of them third was kept for a spare). Accell Extreme voltage Coil Packs, plugs 1 range lower, Wiseco pistons 1/2 atmosphere higher than stock in stock bore.High amperage Stator and rectifier with a flywheel from a 200 were also added (jerry rigged)
With the Prop Ernie gave me to begin with I was running 8.3-9.5 gallons per day running a total of 44 miles per day (22 each way) @ 29mph
With a 4 blade prop I was pulling the same gallons but my speed had dropped to 22mph and I was thresholding the rpm's.
Plotched on a different 4 blade and brought the rpms back down and was in the 8.0-9.1 gallon per day range.
OK so I was not happy by a longshot picked up the quicksilver guide on the internet from Mercury's website, used the prop picker to find out the pitch and diameter I needed. There I was, jumped right into the 10.5 to 11 gallon a day range using the very prop a phone call to their techs revealed was the right one (after not finding my exact model hull on their site). rpms dropped to 4000 even. Tried a same pitch/Diameter Solas Prop and dropped under 11 gallons a day but not by much.
Engine made it onto a Wellcraft Step-Lift V-20 on a short stinger tail.
OK I have had 4 other V-20's over the years and have another I am tinking with at the moment but the difference in mileage between it and the Pro-line should have been dramatic but the engine was under powered for the boat and straining and therefore she was in the 11.5 gallon per day range. But after digging I can give you the following numbers:
'85 Wellcraft V-20 - bilge filled with composite foam, trim tabs added - no other mods
Johnson 300 V-8 12 gallons per hour @ 84mph
'85 Wellcraft V-20 - stock 230 horse Sea drive.
Before tweaking and propping 14 gallons per hour @60mph
after tweaking and propping 9 gallons per hour @ 71mph.
'85 Wellcraft V-20 with Twin 2004 Yamaha 300 2-stroke HPDI's mildly tweaked, 3 extra bids of glass, 2 bids of carbon fiber, 2 bids of Kevlar and 2 bids of Fiberglass added to transom and some of the rear of the boat going forward about 3 feet. Stock tank was removed, entire bilge was filled with composite foam, gunwhales and all cavities around the compartment areas in the cabin were filled with Nitro-cellulose refrigerator foam and glassed back in. Deck drains were increased to 4" diameter with glassed in tubes going directly out the sides. Entire bottom of Hull recieved 1 bid of Kevlar, 1 bid of Fiberglass, 1 bid of Carbon Fiber, 2 bids of fiberglass (tight weave) to 3"above the waterline. the inside of the cuddy got 3/4" of sheet foam, glassed in with 1 bid Fiberglass, 1 bid Kevlar, 1 bid fiberglass. Stinger tail holding the engines was basically a block of styrofoam we hot-wire cut in a stonered afternoon. It had a 2"x1/2" box aluminium frame glassed into channels we had cut in the foam. rear plate was 1" Hardened Aircraft Aluminium plate. The engine cowlings were strengthened and there were 3 2" hoses fitted from the tops to the rear compartment area (where the batteries go) which had had the wooden access door removed and fitted with a floating flap behind a grated intake (so you could punch a bigger wave in a pinch without soaking the engines and ending out dead in the water). A 180 gallon tank was placed on and glassed in with a 9 bid shell and 1" foam cubes were glassed in to the entire remainder of the deck under 1bid fiberglass,1 bid kevlar and 2 bids fiberglass. windshield was replaced with 2 1" thick lexan forward cowling sections from a Kit plane catalog.
Now we are talking a heavy slug of a boat here but this was made for commuting to radar faucilities offshore and there was reason to have a small fast craft with a lot of range. But because she was a bit on the overpowered side she was very economical - This was a boat that would top 100mph on 16 gallons per hour loaded with tools. Kick it back to 50 or so and she pulls 2.4 gallons per hour.
This kind of Effiency comes with a price though. Even though the vessel was heavier and strong enough to take some pretty serious stuff, that 100mph top end was not what the boat would do but rather the point where the front end was feathering to the point of being scary and she was out of the water far enough the trim tabs were useless and she would lay over to the left just a bit - way not safe and not something you really want to be doing intentionally. There was still plenty of throttle left and those hefty Yamahas were not even beginning to strain. .
1985 Wellcraft V-20 with a 250 Merc V-8 on a shorty stinger 8.4 gallons per hour @ 58mph
1979 C-Tremblay tow/mullet boat w/full tunnel drive, bilge area completely filled with composite foam and sealed in with an extra 2 bids of glass over the entire deck and 1 bid over the sides with all through hulls glassed in Plastic fittings.
This is my cousins boat and it is a workhorse dragging 40ft of nets most of the time. But we have guesstimates of empty running consumption and Brian is usually pretty accurate -
90 Horse Johnson 2-stroke 4.9 gallons per hour @ 24mph
155 Horse Johnson Commercial 2-stroke 5.1 Gallons per hour @32mph (about all you can take sitting in the tower - boat will go faster)
So based on the above, it would indicate that the pattern is more powerful engine under the same load requires less fuel?
Same holds true down to your kids 12ft Sun Dolphin - tried it this weekend Took a merc 9.9 short shaft on a 12ft Sun Dolphin and got .7 gallon per hour consumption @ 12 knots. Swapped the Carb and put on a 15 prop and we went to .9 gallons per hour @ 21 knots.
So when picking an engine for your new boat or your next re-power it would seem that one should lean towards maxing out the hulls rated engine capacity. You dont have to go any faster than you would with the smaller engine and you will be straining less at the pump - something to consider when trying to cut dollars on initial engine investment - in the long term under powering will cost you way more not just in fuel but in wear and tear on internal engine components.
If you are considering modding your existing engine remember to keep it simple - highest voltage coils (packs).you can lay your hands on. have the exhaust tuned, and hand pick your prop yourself - test them with you running the boat not with some mechanic running the boat that is going to dial it in for his/her style of running your boat. Pull into the shallows and swap a couple of props out till you find the one that gets you the least amount of gallons per hour based on your own operation of your vessel. If you are thinking it is time for a rebuild anyway - hey there are still marinas that will re-build a powerhead for you and go with a half or even a full atmosphere higher pistons in it - cost is about the same but do it wisely - dont overdo 1/2 an atmosphere is usually enough to reduce your fuel consumption 5% or more. Little thing like good oil at all times makes a difference too. The 15 I use for a kicker on my 21' Carolina runs .8 gallons an hour on quicksilver 2 stroke oil and .7 gallons per hour on Yamalube @6 knots wide open - on her main engine (a 115 Yamaha) she consumes .4 gallons per hour at the same 6 knots consistently regardless of oil brand.
Some of the simplest rules of thumb are:
1: Change your Fluids on time!
Change your boats fluids at the manufacturers recommended service intervals. If you are running the engine(s) wide open all the time cut it in 1/2 (IE: a every 100 hour service - you need to be doing every 50).
your engine has been stored for more than 5 or 6 months - BEFORE YOU USE IT OR EVEN TRY TO CRANK IT change all your fluids - this includes the oil in your 2 - strokes reserve tank - even if it is inside the engine like on the smaller engines. This ensures you are going to get proper lubrication from oil that has not lost its viscosity or began to break down from age (YUP 2-stroke oil breaks down from sitting around too) 4-stroke guys, change your crankase oil. all ya'all change your lower unit oil with good gear lube (trust me don't scrimp pennies - get the best gear lube and the best oil you can for your engine every time and it will treat you right and run at or closer to its top performance level at all times.
Change out your gas too - or at the very least, if you insist on trying to "run it through" with any gas more than 6 months old - do yourself a favor... put in some Sea Foam, Ring Free, Marvel Mystery Oil or even some good old fashioned STP if that is all you can lay your hands on.. If you are running a 2 stroke - go a little heavy on the oil like if you normally run 50:1 drop it to 40:1 - if you are oil injected or otherwise using some sort of automatic oiling system, I would lean towards just adding 1/2 pint Marvel Mystery Oil for every ten gallons of gas directly to the gas and have 2 spare sets of plugs handy - run out at least 1/4 tank and get somewhere you can dump in the highest octane gasoline you can lay your hands on - hey if you know it is going to be a marina make sure you carry some quality octane booster along and just put in 1/2 the recommended ratio. Then run it down to 1/2 top it off again and you should be allright as long as you run that tank through. I cannot stress enough though how bad an idea it is to try to "run it through" with gas that has passed the 6 month mark - even with the additives you run the risk of gumming up your carbs and being one of the people I am towing home after a bad day of nightmare boating (and dont think I am joking about old lower end lube wrecking folk's day either)
3. Spark Plugs - Keep 'em Fresh
Dont worry so much about the manufacturers service interval other than as a general guideline - change them on the manufacturers service interval for sure BUT: if your engine starts stumbling before the service interval, change your spark plugs out (always make sure your wires are pristine too - no such thing as cracking or any sort of a worn spot being acceptable in a salt water environment. A high Voltage Ignition system such as those made for performance applications comes in handy for the average guy as well. These system can and I emphasize "can" improve your fuel economy up to 20% when coupled with the right set of plugs. In the real world the mileage or decrease in hourly rate of consumption seems to be more along the lines of 9-12% for most applications. Now what I mean by when coupled with the right set of plugs is this: I will take out the charts in our local autozone, find the heat range I am in - thread diameter and length of threads then I get plugs in the same heat range and thread configuration from a few different manufacturers. If possible I like to stay with ACCEL Super coils (part number 140001and adapt if at all possible or part number 140008 if I just cant get out of using a coil pack/electronic style - they do make Excellent CDI units too) Mallory 9mm solid core blue wire with the best spark plug boots I can lay my hands on. Usually you can pick up the older style Johnson boots fairly cheap and they are more than heavy enough to carry the coil - Yamaha spark plug boots are really excellent too. Plugs wise I like Bosch Platinum +4's but they are hard to match up for some older applications. What I had to do with my old Merc's was to get some split fires that fit and were one heat range lower (You nearly always want to drop your plugs a heat range when going with hot coils) What I finally had to do was pop in a depth micrometer, make sure I had the piston on TDC and hand turned a Bosch Platinum+4 plug of the appropriate heat range with just a bit of soft wax on the end of the tip of the plug to make sure there was no contact (turned out I had quite the room to spare in fact) between the top of the piston and any part of the tip of the plug. these were like 2 threads longer but one of the mechanics at Marine Dynamics had a set of used metal spark plug washers from a set he had just pulled and that seemed to make up for it nicely -worst I did was bump up the compression a bit to boot. Ran like a raped ape but I ate through those plugs in about 20 hours. Went to Ringfires after that and got 10 or less hours out of those before performance degraded to intolerable and I stuck in a set of NGK platinums.Ran great plugs lasted about 40 hours stayed with them from then on. But you have to decide what is best for your own engine based on your own research and tinkering and please use good judgement.
4. If your engine is for some reason not covered by warranty - hey another thing to consider may be mildly shaving your heads and having everything matched and polished - It is a permenant gain, if you still have a fairly fresh set of pistons and rings you should be able to eke out mild, permanent gains horsepower wise but these thing usually go a long way towards good economy. Make sure you re-tune and if need be re-jet your carbs if you do this. put in a glass test plug and get it tuned in to a nice bunsen blue. If possible, use a and infrared or other thermal sensor and measure the head temperature to make sure you are not running too hot - go richer or go with colder plugs if you are. - 2-strokers can benefit greatly from a nicely polished and matched reed block as well. If you hook up with the right mechanic or parts guy who has tinkered in the background often times they can tell you which reeds are going to be better for what you are trying to do and will generally make sure by verifying what type of boat you have and what you do with it - ALL of these factors are important whenever you even consider going with non-stock, Super-Stock or Aftermarket reeds - you also have to have a parts guy willing to spend a lot of time looking up exactly what you need - there is not exactly a complete cross reference or an all in one guide for swapping, so they have to look them up by measurements - this is time consuming as most of the parts books are intended for referencing stock reeds (OK there are a couple of so so but nowhere near complete references out there and then only to the normal application) In other words if you get a parts guy to look all this up for you - be nice let him be the parts guy to order them in for you.
If you are re-building your powerhead anyway, take the extra time (or spend the extra cash) and have it balanced and blueprinted. Yeah it takes a lot of time (or costs a bit of jing) but in the long run when you consider all the time you run an engine.... it improves the overall longevity of the engine, it improves your fuel economy in that it helps your engine run more efficiently.
All of the above is just observations, Call it redneck hoodoo, simple things that work, whatever....I am in no way advising you in any way shape or form. You are welcome to add your own observations and theories as comments.