Optimax improvements prop, rpm, gph

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Jaysen
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Optimax improvements prop, rpm, gph

Post by Jaysen »

TomW1,

Helping a buddy with a trophy 2103 (21’ CC) powered with a 2008 Mercury 200hp optimax. Current prop is 15p three blade. Boat is 3500. Typically runs 110gal fuel and 20gal fresh water, 20gal salt water (bait well).

The fuel consumption seems to be “high” at 8gph at 4K rpm and about 32mph. The sucker jumps out of the hole onto plane which is nice (2stroke win!). Motor has no record limiter but we know the top end is 5750. I ran out of testicular fortitude long before we reached that (buddy was fetal position on the deck at 4800).

Any ideas on how he might get better fuel numbers? He is clearly willing to give up some top end speed.

Thanks.
My already completed 'Lil Bit'. A Martens Goosen V12 set up to sail me to the fishing holes.
Currently working on making a Helms 24 our coastal cruiser.
“Mark Twain/Samuel Clemens” wrote:Eat a live frog first thing in the morning and nothing worse will happen to you the rest of the day.
Jaysen wrote: Mon Apr 29, 2019 3:44 pm I tried to say something but God thought I was wrong and filled my mouth with saltwater. I kept my pie hole shut after that.

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Re: Optimax improvements prop, rpm, gph

Post by TomW1 »

Jaysen wrote: Thu May 06, 2021 10:41 pm TomW1,

Helping a buddy with a trophy 2103 (21’ CC) powered with a 2008 Mercury 200hp optimax. Current prop is 15p three blade. Boat is 3500. Typically runs 110gal fuel and 20gal fresh water, 20gal salt water (bait well).

The fuel consumption seems to be “high” at 8gph at 4K rpm and about 32mph. The sucker jumps out of the hole onto plane which is nice (2stroke win!). Motor has no record limiter but we know the top end is 5750. I ran out of testicular fortitude long before we reached that (buddy was fetal position on the deck at 4800).

Any ideas on how he might get better fuel numbers? He is clearly willing to give up some top end speed.

Thanks.
Nice boat, nice motor, Okay, lets get me some more information. Do you know what the pitch of the prop is. It will be on the barrel of the prop next if you don't know it. Next do you know the weight of the boat as it leaves the dock that means hull, passengers and gear, fishing, anchors, coolers. I need these weight numbers as close as you can get them. You have given me the motor, and liquid amounts so can get the weights from them. I looked up the dry weight of the Trophy 2103 and the factory said 3380 for dry weight. So start there not 3500lbs unless he has added t-top and other accessories.

Also do you have the current top speed, I know it is a knee shaker but it would be a help. 5750 is max rpms for the Optimax 200.

Once I get all this I will run the numbers.

Glad to help out Jaysen, take your time and be as accurate as you can.

Sounds like he has a good fishing rig.

If you have any questions ask.

Regards Tom
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses. LT US Navy 1970-1978

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Re: Optimax improvements prop, rpm, gph

Post by TomW1 »

Jaysen reading through your notes again I noted that you gave me the pitch at 15. so I think I have enough info to run some numbers to at least get a preliminary result. Let you know in a little while. But I will still need the numbers I asked for, passenger weight, gear weight and miscellaneous weight. For this run through I will use 2 passengers at 175 for 350lbs, 250lbs. gear weight an 200 miscellaneous..

Tom
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses. LT US Navy 1970-1978

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Re: Optimax improvements prop, rpm, gph

Post by Jaysen »

Thanks Tom. We are still trying to figure out the “gear load” as he is changing his current setup completely. Hope to have the numbers by this weekend.

On the human front… plan for three please. 175 would be the correct weight though.
My already completed 'Lil Bit'. A Martens Goosen V12 set up to sail me to the fishing holes.
Currently working on making a Helms 24 our coastal cruiser.
“Mark Twain/Samuel Clemens” wrote:Eat a live frog first thing in the morning and nothing worse will happen to you the rest of the day.
Jaysen wrote: Mon Apr 29, 2019 3:44 pm I tried to say something but God thought I was wrong and filled my mouth with saltwater. I kept my pie hole shut after that.

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Re: Optimax improvements prop, rpm, gph

Post by TomW1 »

That is fine Jaysen. I will be travelling over the week end so won't be back on line till Monday or Tuesday. Some of the Gear is probably already included in the weight of the boat. Fuel lines, electrical lines, lights and anything that came with the boat. So any thing that he added after he bought the boat and is permanent. I have actually built the model up and the fuel weight and water weight is in as well as the hull and motor weight and specs. so just waiting for your weights for boat if you want to adjust from 3500 and then the gear and miscellaneous weights.

So will wait to get what you send when I am back up Monday or Tuesday.

Regards, Tom
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses. LT US Navy 1970-1978

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Re: Optimax improvements prop, rpm, gph

Post by TomW1 »

Evening Jaysen.. Writing to you from our cabin on the Mississippi River cabin in Iowa. I have run two different calculators now with the numbers for gear of 200 and Misc. of 200 plus all the numbers you gave me and the numbers I got from Mercury for the Optimax. Total weight of the boat as loaded was right around 5500lbs as she left the dock with 3 people. Top speed was about 40 miles an hour. Both models showed a 15 pitch prop was the correct one. What I can recommend to slow her down some would be to go to a 4 blade prop. You will lose 3 maybe 5 miles mph, but also increase your handling in heavier seas and increase your straight line steering. Mercury has a Revolution 4 if he wants to stay with Mercury.

Well that is all for tonight. Let me know when you guys get the final numbers. I'm just laid back watching the old man river flow by for the next 3 weeks. :D

Tom
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses. LT US Navy 1970-1978

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Re: Optimax improvements prop, rpm, gph

Post by fallguy1000 »

Best way to deal with a gas hog is to get on plane and back off. The chart for fuel economy always worsens. Many guys think once on plane to hit it and to faster, but a boat drinkin fuel like that is hard on the wallet and the range.

Now and then the sweet spot can be a tad higher, but he needs to test the setup just on plane.
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Re: Optimax improvements prop, rpm, gph

Post by Jaysen »

fallguy1000 wrote: Thu May 20, 2021 8:19 am Best way to deal with a gas hog is to get on plane and back off. The chart for fuel economy always worsens. Many guys think once on plane to hit it and to faster, but a boat drinkin fuel like that is hard on the wallet and the range.

Now and then the sweet spot can be a tad higher, but he needs to test the setup just on plane.
Yeah... I'm in that camp, but he's under the impression that RPM zones are more critical. The fact that the motor manual says that makes it hard to argue with him.

We killed about 100gal before I posted this and had maybe 110mi. A lot of that was pounding in 3'+ 10mi out and high speed "how fast can we safely move" in various states of chop. I think it will seem less awful to him after he's more skilled at driving. I routinely had better fuel numbers than he did for the same speed/conditions. I was lighter on the trim though.

Tom, I'm still trying to get him to commit to a plan. He keeps changing ttop plans and the like. I think numbers you have match what the boat was speced with as the current prop is a 15p. I'll try to beat Adam into submission this weekend.

Thanks!
My already completed 'Lil Bit'. A Martens Goosen V12 set up to sail me to the fishing holes.
Currently working on making a Helms 24 our coastal cruiser.
“Mark Twain/Samuel Clemens” wrote:Eat a live frog first thing in the morning and nothing worse will happen to you the rest of the day.
Jaysen wrote: Mon Apr 29, 2019 3:44 pm I tried to say something but God thought I was wrong and filled my mouth with saltwater. I kept my pie hole shut after that.

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Re: Optimax improvements prop, rpm, gph

Post by Fuzz »

Jaysen my SeaSport, that you were on, will get between 2-3 miles per gallon. There is a sweet spot where the boat is up on plane and running clean where it gets the best mileage. From there the faster I go the worse the mileage is. If you buddy it getting 4 miles to the gallon that is not bad and he may not be able to do much better than that.

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Re: Optimax improvements prop, rpm, gph

Post by TomW1 »

Fuzz wrote: Thu May 20, 2021 3:05 pm Jaysen my SeaSport, that you were on, will get between 2-3 miles per gallon. There is a sweet spot where the boat is up on plane and running clean where it gets the best mileage. From there the faster I go the worse the mileage is. If you buddy it getting 4 miles to the gallon that is not bad and he may not be able to do much better than that.
Fuzz thanks for doing the conversions, I forgot to do that. You are correct 4 miles to a gallon at 32 mph is not unreasonable with an Optimax. They were not known as fuel savers as I recall especially with that load. Jaysen just tell him to slow down a little to see if that will help his mileage. :D I would say 4000 rpm is pretty high to be in the sweet spot for mileage. Most boats I have propped are in the 32-3600 rpm range. Not all, but most.

Tom
Last edited by TomW1 on Thu May 20, 2021 4:05 pm, edited 2 times in total.
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses. LT US Navy 1970-1978

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