Twins to single - Page 2

RIBS! · 21 October 2016, 02:41

Ok, so those numbers make sense that a 250 4.2 L is pretty close to the 300 4.2 when running 87 octane which is what I get at our fuel dock so looks like I have options on my new motor especially since based on what i'm hearing my twins probably equal a single 250 in hp at the prop. I'm glad to here a 300 with 87 oct is pushing a 4.5 ton Northbank at 35 mph at 4500 rpm. I like to run mine at 3300 to 3500 on our trips so based on the weight difference sounds like I can probably be moving at 25 + mph at 3300 with either the 300 or even the 250 at 87 oct.
I haven't weighed my boat but was told its 4400 pound dry based on military spec so when I add 2000 pounds for 13 passengers based on 150 pds average weight, 1000 pds fuel with both tanks full, 800 pds in twin engines and 500 pounds in new passenger seating and gear brings me to my estimate weight of 8,700 pounds. i'm sure im a little off somewhere since its just guessing but I cant imagine i'm less than 8000 pds fully loaded.
I attached a pic of the boat with just 7 people on it and and fuel not topped off so you can see it has some weight to it.

jonp · 21 October 2016, 08:52

Quote:

Originally Posted by ncp

Interesting...

Common wisdom over here (who know if it's right or wrong) is that because the octane does break down, start with the higher octane if your going to store it for long periods.

Ribs, those motors look low in the water, didn't realise they were military spec, no wonder they are so heavy compared to the pro etc.

Spoke with one of Australia's biggest dealers today who told me to run it on regular petrol unless I simply wanted to spend more money, the higher octane wouldn't harm the engine just my back pocket. He said the engine revs out to the same rpm as a 70 or 90 5800-6300 and not 8000+ like a race engine.

Had a quick look and found this article from your side of the pond which was basically what dealers and mechanics quote here, the part about storing a boat even for a month might be interesting for those who don't get out to often.

All About Outboard Gasoline | Salt Water Sportsman

Jon

ncp · 21 October 2016, 18:29

Quote:

Originally Posted by RIBS!

when I add 2000 pounds for 13 passengers based on 150 pds average weight

Is this vessel coast guard inspected? I though you guys only did 6-pack charters?

RIBS! · 22 October 2016, 00:01

Yeah, I feel the engines are a bit low as well. I'm thinking if I get a 30" shaft I can hopefully have a few inches to spare so I may get a jack plate to raise it a little bit.
Yes, we have been running 6 packs for 10 years now but finally after a long drawn out and expensive project we are wrapping up the Coast Guard process to carry 12 plus 1 on this boat. Not sure if ill take on another COI on my other boat.
Probably easier to just find one already certified.

ncp · 22 October 2016, 00:06

Quote:

Originally Posted by RIBS!

Yeah, I feel the engines are a bit low as well. I'm thinking if I get a 30" shaft I can hopefully have a few inches to spare so I may get a jack plate to raise it a little bit.
Yes, we have been running 6 packs for 10 years now but finally after a long drawn out and expensive project we are wrapping up the Coast Guard process to carry 12 plus 1 on this boat. Not sure if ill take on another COI on my other boat.
Probably easier to just find one already certified.

Ya, that's going to sit even lower than your picture with more weight. I'm sure you have, but you've talked others in you industry who run 12+1 on a 733 to see how they're set up? (there has to be guys in Canada that do it).

I heard from talking to Russell that the whole process is a complete PITA and took forever with his Northwind.

RIBS! · 22 October 2016, 00:53

Yeah, I'm concerned about that engine height. Cool thing is when the boat fills up they will have to use the tandem jockey seats next to the captain and on the bow so hopefully it will balance out instead of going deeper in the back.
The process is definitely a PITA. I saw Ryan Pratt did one for 17 + 1 on a 733 so shouldn't be an issue with weight.

jonp · 22 October 2016, 01:55

Another good place to look for performance is on this Yamaha site in the US, you should be able to find some sort of boat close to your size and weight. There are heaps of performance tests here Outboard Performance, Performance Bulletins | Yamaha Outboards

ncp · 22 October 2016, 03:38

Oh, and guess what Russell runs on his Northwind?

A 4.2L 250 HP.

RIBS! · 22 October 2016, 03:58

I'll check out those stats on the Yamaha site, Thanks
Yeah, Russel's boat is pretty fast too with that 250. My boat is a little heavier than his but I think it should be fine.

Bigtalljv · 24 October 2016, 00:50

So I paid a little more attention out fishing today. With four people, 750lbs worth of people, and 20 gallons of gas.

28mph, 3800 rpm, 10gph
40mph, 4800 rpm, 13gph

HUMBER P4VWL · 24 October 2016, 08:31

Quote:

Originally Posted by RIBS!

Yeah, I'm concerned about that engine height. Cool thing is when the boat fills up they will have to use the tandem jockey seats next to the captain and on the bow so hopefully it will balance out instead of going deeper in the back.

The process is definitely a PITA. I saw Ryan Pratt did one for 17 + 1 on a 733 so shouldn't be an issue with weight.

If this is a tour operation do you not need LJs on to comply?

Poly · 24 October 2016, 10:34

Quote:

Originally Posted by HUMBER P4VWL

If this is a tour operation do you not need LJs on to comply?

You wouldn't in the UK. In fact even in Ireland where wearing LJ's is compulsory for some leisure users, I think a boat this size would not be compulsory.

jwalker · 24 October 2016, 12:11

Quote:

Originally Posted by Bigtalljv

So I paid a little more attention out fishing today. With four people, 750lbs worth of people, and 20 gallons of gas.

28mph, 3800 rpm, 10gph
40mph, 4800 rpm, 13gph

That's interesting, you're more economical travelling at 40mph!

As for the engines, a larger capacity motor will have more mid range power and that is where it counts for carrying a load. Whether the 250 is as good as the 300, you need to see the power or torque curves to see which is better for you at the rpm you normally cruise at. I certainly wouldn't make a decision based of what someone else happened to fit to their boat!

RIBS! · 24 October 2016, 22:30

That info helps on your actual speed verses RPM.
I do feel that with my boat carrying 3 times the passenger weight, 7 times the fuel weight and possibly even a much heavier hull based on Mill spec verses non military hull I am probably about 2500 pound heavier than your boat give or take so your numbers would change drastically on my boat with the same engine. Out of all the applications i have seen there has not been one where a single engine was pushing an 8500 lb boat which is concerning me now about switching from twins to a single even though I really would prefer a single.
I'll keep looking for actual single engine applications on such a heavy boat.
As for the question about if life jackets are required to be worn on charter boats the answer is no.
Type 1 life jackets need to be on board for all passengers but not mandatory to wear them except for children 13 and under.
We do ask our customers to wear them when we go offshore just for added safety.

Bigtalljv · 24 October 2016, 23:15

My boat is ex-military also. My boat weighs as much if not more than yours. Rumor has it the 733 have cored hulls and mine is 3/4" of solid fiberglass.

Come on by with 10 or 12 buddies and we can give it a try.

Jason

RIBS! · 25 October 2016, 00:20

Good to know. Ok,great. Look for a short bus coming your way with me, 10 friends and a big cooler of beer. Thanks for the help!