Large FE Tunnels (gas size)

[HTV Boats]

Wennie Bester posed some questions over in an FE how to thread in the Outboard forum that may get more experienced information here.

The basic idea is doing a gas sized tunnel (49+ inches) and the comparison of what hardware might work to replace a gas motor. Also Wennie questioned runtime of 7-8 minutes?

Starting with run time I don't think minutes is what we try to do. For racing purpose 7-8 laps will finish a heat. This is one of the big drawbacks to Internal combustion converts to FE. Run time is dictated by load. A boat that will run say 50MPH for a heat race will have to be propped down to say 40MPH to gain significant run time. Above 4 minutes on plane at speed just isn't realistic. So racers limited to 6-8 laps then a battery charge or change to stay at the higher speed go back to their fuel boats. I have heard the "is that all the run time you get" quote more than once.

Now to compare a large tunnel, gas vs FE.

My gas tunnel was over 20 lbs. The 26cc powerhead with pipe around 5lbs. on a G-Morty weighing about 3 lbs. To be fair maybe 1 pound of fuel to run quite a few laps and 4-5 minutes easily.

If I was going to build a comparable FE tunnel I would use a larger 56mmX100 or so motor. Bang for the buck a Castle 2028 on 10S with a say 300amp Swordfish ESC would easily outpower the gas motor. For comparison I will use current OSE prices. Castle 2028 $240 and weighs 2.75 lb. 300 SF $290 and one pound. Batteries from Dinogy 4 5000ma 5S packs to make 10000ma of power (Namba limit) would weigh aprox 6 lbs. and cost $132 per pack or $528. That makes under 10 pounds of hardware which only 3 (plus the G-Morty) are hanging off the back. About $1150 for the power. A Quickdraw with pipe is in the $900 + range.

On 10S a 2028 Castle (800kv) will spin 29600rpm (no load) and probably 23,000 on the water. Power should be in the 7-8 HP range. As for props probably more pitch and less diameter than gas. Again their will be many other workable options here and please jump in with opinions or experience with larger FE motors. I like the Castle for price, power, quality and with a finned case you don't need a cooling jacket as an outboard where it will get more cool air flowing over it than is a car that it was designed for.

Their may be some thread over on OSE about larger mono's and Cats using similar power.

Mic

 

[CapeTown73]

Thanks so much for kick-starting this thread Mic. I have already learned from what you have posted. The mere fact that you seem to be talking as if such a project is feasible, is already very encouraging.

I just want to clarify my mentioning a 7 to 8 minute run-time (read race-time). All heats for our gas classes here race for 15 laps on a fairly large 'M' shaped course (four right turns and one left). So I had simply been thinking about the option of (initially if permitted) racing an electric powered boat against the current gas powered OB tunnel boats, and I would not envisage me being able to convince the gas pilots to run for a shorter race-time simply because the electric boat can't race further than say 8 or 10 laps.

I look forward to many more interesting posts.

Cheers,

 

[Kris Flynn]

Wennie, you do not have a 10,000MaH limit on your batteries over there, do you?

To run 7-8 minutes at good speeds will put a high strain on the equipment (mainly the ESC). you will want as much MaH as you can fit in the boat (like 12,000+) IMO

Would love to see this thing go

 

[RaceMechaniX]

Wennie,

From my experience running 4 min offshore races with a 10S open cat, you are going to need a lot more capacity which is going to add a lot of weight. I run 10,000mAh 10S2P with a Neu 2215 motor. After 4 minutes I have practically used 90% of the battery. The cat weighs around 20 lbs with batteries. Legally I can run 12Ah total, but having specific batteries for the one class if prohibitive. With a 2028 or similar Scorpion like the 5035/760 you will need 20Ah total.

Tyler

 

[CapeTown73]

Hi Kris and Tyler and thanks for your feedback.

No Kris, we don't have any established rules or specs at the moment (that I'm aware of), because we don't race electrics at any of our clubs, again as far as I am aware. But already I'm starting to doubt the financial practicality of trying to race a 20 pound (or more!) electric boat for 7 or 8 minutes. I've been looking on the web at the sort of equipment that Mic mentioned in his starter post and on OffShoreElectrics.com the cost of a comparable motor + ESC + just one set of batteries, is really frightening, between $1,000-00 and $1,200-00!!!

But I would still welcome any other theories or experiences please.

 

[Joern Markset]

I think the price of an electric set up is fair enough, you may be able to charge the batteries like 500 times, thats like 2,5 bucks a trip... Really cheap
I`m gonna use a pair of the Gens Ace tattu 22000 mah in my 1/4 scale tunnels, they should be able to give you the runtime you ask for.

Btw, do you have any videoclip from your racing? I like when you say that you run M style course, that is how a tunnel should be driven IMO.

 

[Gilbert Pun]

That is interesting!

I have a couple of spare 2028 and Castle 200Hv ESC in the workshop awaiting for the next mission, after installing a couple of the same on the 50" Mono hulls and one set in a gas scale hydro boat they all are running great.

Like to see video clips of FE on a gas size tunnel boat.

 

[CapeTown73]

[SIZE=12pt]Hello Joern and Gilbert, and thank you for your comments. [/SIZE]

[SIZE=12pt]As I’m writing this post on Christmas morning, it is just right that I first wish everyone a blessed day today with friends and family. [/SIZE]

[SIZE=12pt]That Tattu is most certainly an impressive LiPo pack. As a 6-cell with a 22 amp capacity rating, it looks like the sort of pack that could very well provide the required race time. [/SIZE]

[SIZE=12pt]The first YouTube link below shows a video taken with an old phone camera in August this year, and is unfortunately not very clear. However, it starts with the final milling lap with three of us almost going over the start line before the computer race-start signal. My boat (with the orange cowl) starts in third position and by the end of the first lap my boat had passed the other two but it unfortunately did not finish the heat as the pipe mounting started coming loose around 10 laps into the race. But it was still running very well in that heat. It is powered by a 29.5cc Quickdraw Pioneer.[/SIZE]

[SIZE=12pt]The second video is better quality, and shows a few practice laps with the same boat.[/SIZE]

[SIZE=12pt] Gilbert, I would also love to see any photos or videos of an FE (gas-sized) outboard tunnel but up to now no-one has yet come forward with such a boat. Some may disagree with me, but an FE inboard ‘tunnel’ unfortunately just isn’t the same thing as It’s really just a cat with an F1 cowl. I hope to still see someone with a gas sized FE OB tunnel chiming in here with some photos or video.[/SIZE]

https://www.youtube.com/watch?v=flFnCdpiGPc

http://youtu.be/Zb3Fe8ghCTg