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Old 20 August 2013, 02:32   #1
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FC470 - Dive boat considerations?

I picked up a 1990 FC470 to replace my woefully small Avon Rover 315.

It is a complete boat : rollup floor, no transom rot, all of the valves are in place...it holds air for about a day. During my initial wash, I discovered one of the valve bases leaking, and two pinholes. Also, it doesn't feel like the speed tubes are inflated to the same pressure as the main buoyancy tubes...they feel much softer by comparison. I use a Bravo 12 BST electric HP pump to pump the boat up to about 3.5 psi.

My question though : I will be using the boat for diving and transporting equipment to remote places. I would like to carry 3 divers + 12 gallons of fuel.

What size outboard would be the best match? I have access to a 70s Mercury 50 hp jet for cheap..about $300. But, I'm not sure if it is the best match.

Ideally, I would like to do about 22 mph+ with 3 divers.

I am on the Great Lakes here in Michigan.
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Old 20 August 2013, 10:55   #2
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Jets are pretty inefficient. "Safer" than props, but inefficient. An we won't talk about weird handling characteristics (though I assume experience gets you over that one.)

I'd be looking for a 40 to 50 hp outboard. Fuel and dive gear as far forward as possible, divers at the back for comfort.

I used to run a 14' Achilles (aluminum floor) with Honda 40; the 4 to 5 diver load range wanted a bit more oomph (well to be fair, 4 divers did; 5 was definitely underpowered. And over stuffed as far as deck space went.)

If there's a hull plate with max hp, go for that.

jky
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Old 20 August 2013, 11:05   #3
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Welcome to Ribnet,

Check speed tubes factory recommended pressure, 3.5 psi seems to low, probably needs more for top rigidity. Min 40, max 50 HP engine would be the way to go for that size boat and diving gear.

Happy Boating
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Old 20 August 2013, 11:06   #4
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Might peruse this thread as well:
Engine Capacity for Zodiac FC-470

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Old 20 August 2013, 11:40   #5
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12 gals is a butt load of fuel. I have a 60hp Yam (4 stroke) with a 12 gallon tank - range is about 80 miles with that combo. Realistically, alot further than you want to go from safe harbor. If you can get a 9 gallon tank you'll save a bunch of weight and space. Or a 6 gallon + a 3 gallon you only bring along when you actually need it.

Ditto what jyaski said on a jet drive. That Merc 70hp will guzzle fuel and you will end up at full throttle alot too. There's a reason its only $300! I would look for a 50hp 4-stroke propped outboard instead.

You will probably do 22mph with 3 divers and a 50hp, but only if its flat calm.
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Old 20 August 2013, 23:43   #6
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Quote:
Originally Posted by jyasaki View Post
Jets are pretty inefficient. "Safer" than props, but inefficient. An we won't talk about weird handling characteristics (though I assume experience gets you over that one.)

I'd be looking for a 40 to 50 hp outboard. Fuel and dive gear as far forward as possible, divers at the back for comfort.

I used to run a 14' Achilles (aluminum floor) with Honda 40; the 4 to 5 diver load range wanted a bit more oomph (well to be fair, 4 divers did; 5 was definitely underpowered. And over stuffed as far as deck space went.)

If there's a hull plate with max hp, go for that.

jky
Hull plate specifies max 40 hp for the rollup, although up to 65 hp with the rigid aluminum floor.

Nevermind about the $300 70s Merc 50 hp jet, it turns out it has a 15" shaft.

Quote:
Originally Posted by Locozodiac View Post
Welcome to Ribnet,

Check speed tubes factory recommended pressure, 3.5 psi seems to low, probably needs more for top rigidity. Min 40, max 50 HP engine would be the way to go for that size boat and diving gear.

Happy Boating
Factory specs call for 3.5 psi.

Quote:
Originally Posted by jyasaki View Post
Might peruse this thread as well:
Engine Capacity for Zodiac FC-470

jky
Already read it! Thread digresses pretty fast and doesn't yield too much info.

Quote:
Originally Posted by captnjack View Post
12 gals is a butt load of fuel. I have a 60hp Yam (4 stroke) with a 12 gallon tank - range is about 80 miles with that combo. Realistically, alot further than you want to go from safe harbor. If you can get a 9 gallon tank you'll save a bunch of weight and space. Or a 6 gallon + a 3 gallon you only bring along when you actually need it.

Ditto what jyaski said on a jet drive. That Merc 70hp will guzzle fuel and you will end up at full throttle alot too. There's a reason its only $300! I would look for a 50hp 4-stroke propped outboard instead.

You will probably do 22mph with 3 divers and a 50hp, but only if its flat calm.
I was planning on twin 6 gallon tanks, that way I can take one out for short outings, and add the second tank for big trips. I was planning on doing the 35 mile trek from the Keweenaw peninsula to Isle Royale for some camping. I figured it'd make for a nice "man weekend" with the guys.

Side note:
Does anyone know what threading the rapid fill valves are? I'd like to adapt them to 1/4 NPT so I can make my own rapid fill system for 1/15th the price.
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Old 21 August 2013, 11:28   #7
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Quote:
Originally Posted by office888 View Post
Already read it! Thread digresses pretty fast and doesn't yield too much info.
Yeah; should have mentioned that...



Quote:
I was planning on twin 6 gallon tanks, that way I can take one out for short outings, and add the second tank for big trips.
Sounds reasonable. I'd look at it more as a 6 gallon, with an additional 6 as an as needed option. Doubt you'll be burning more than 6 gallons on a trip on a regular basis (but that depends on your trip planning.) My SIB used to run all weekend on a 6 gallon tank.


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Old 21 August 2013, 11:52   #8
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Quote:
Originally Posted by office888 View Post
Side note:
Does anyone know what threading the rapid fill valves are? I'd like to adapt them to 1/4 NPT so I can make my own rapid fill system for 1/15th the price.
I tried this with my halkey roberts valves. Its didn't really work and the tube pressures ended up uneven. I don't totally understand why; I stopped testing because one tube was consistently over pressure and I was afraid of damaging it. I suspect the spring pressures between valves were significantly different and the air was preferentially taking the path of least resistance.

I use a scuba tank to fill my valves off a BC inflator hose. Making a BC nipple to boat valve adapter was one of my best ever projects. I can top up my 15.5 ft boat with a 13cf airgon bottle. If it needs more than topping up I use an old 1800psi lp50 that a friend gave me.

I think 2x gal is about right. I have a single 12 gal tank and rarely even use 1/2 of it.
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Old 21 August 2013, 22:19   #9
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Quote:
Originally Posted by captnjack View Post
I tried this with my halkey roberts valves. Its didn't really work and the tube pressures ended up uneven. I don't totally understand why; I stopped testing because one tube was consistently over pressure and I was afraid of damaging it. I suspect the spring pressures between valves were significantly different and the air was preferentially taking the path of least resistance.

I use a scuba tank to fill my valves off a BC inflator hose. Making a BC nipple to boat valve adapter was one of my best ever projects. I can top up my 15.5 ft boat with a 13cf airgon bottle. If it needs more than topping up I use an old 1800psi lp50 that a friend gave me.

I think 2x gal is about right. I have a single 12 gal tank and rarely even use 1/2 of it.
The FC470 is a Zodiac Milpro boat. It is also known as the "Futura Commando". Mine is a military surplus model and is equipped with the "rapid inflation" system. However, I'm missing the bottle, regulator, hoses, and adapter. I do have installed the OPVs, inlet check valve, and the wrap that secures the bottle near the transom.

Basically, for a mere $2000, you can purchase a SCUBA 1st stage, two QD hoses, and two special adapters. The entire boat can be filled with an AL80 / 12L tank. It actually overpressurized the boat, and the OPVs let out the excess.

I'm simply missing the Zodiac kit...However, I have a junk old Sherwood Brut 1st stage, a few BC hoses, and access to fittings.

A machinist friend of mine is going to turn some adapters for me...inlet check valve-to-1/4 NPT. Then I'm going to get some 1/4 NPT BC fittings. Click click and I can inflate the whole boat easily for less than $200.

The FC470 has special intercommunicating valves. You rotate the valve and it has settings. You can inflate chamber A, inflate chamber B, both chambers, or neither chamber. It has 4 of these valves. If all are set to "both" you can inflate the entire boat from one valve.

The twin 6 gallon also mandates a turn point!

Quote:
Originally Posted by jyasaki View Post
Yeah; should have mentioned that...





Sounds reasonable. I'd look at it more as a 6 gallon, with an additional 6 as an as needed option. Doubt you'll be burning more than 6 gallons on a trip on a regular basis (but that depends on your trip planning.) My SIB used to run all weekend on a 6 gallon tank.


jky
A typical dive trip around here is about 16 miles round trip. That translates to about 1.5-3 gallons of fuel. That means I can have a good size reserve with a single 6 gallon, yet without compromising weight!




This is the boat!

And now the secret is out...yes, I work for an inflatable boat dealer. Lately, we have been selling a lot of smaller AB inflatables. We deal Zodiac, Achilles, Mercury, and Newport Vessels (cheapo chinese boats). I am the primary sales monkey. I am also the secondary repair guy.
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Old 22 August 2013, 02:10   #10
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Quote:
Originally Posted by captnjack View Post
12 gals is a butt load of fuel. I have a 60hp Yam (4 stroke) with a 12 gallon tank - range is about 80 miles with that combo. Realistically, alot further than you want to go from safe harbor. If you can get a 9 gallon tank you'll save a bunch of weight and space. Or a 6 gallon + a 3 gallon you only bring along when you actually need it.

Ditto what jyaski said on a jet drive. That Merc 70hp will guzzle fuel and you will end up at full throttle alot too. There's a reason its only $300! I would look for a 50hp 4-stroke propped outboard instead.

You will probably do 22mph with 3 divers and a 50hp, but only if its flat calm.
Interesting. I was going to ask why so little fuel if planning to travel to go to remote locations. I typically carry 4-5 x 5 gallon tanks on my trips which gives me a range of 100-125 miles (~ 5 mpg). That is with a 40 hp 2 stroke ran at WOT for 80-90% of the time which is considerably less fuel efficient a 60 hp 4 stroke would be.

I find the range I get with this set up can be quite limiting at times and for a number of trips I have to make sure to plan ahead as to where I would be able to re-fuel. Calling ahead to remote lodges to see if I can purchase fuel at those locations is often done. The main problem with purchasing fuel at remote locations is that you pay through the nose (about double) to do so.

I would suggest that when planning your deck for passengers, gear and fuel, be sure to reserve some space for at least an additional 12 gallons, should it be needed.
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