Thread Tools
Oct 28, 2019, 02:41 AM
Just a Balsa Building CL flyer
Thread OP
Discussion

Old newbie needs OS .91 FSR help/advice 1.0


Question #1) Anyplace in the Los Angeles area people are just getting together and running boats for sport? (Other than Legg Lake - Those guys were WAY too self-centered (Sorry: “too busy”) to help a newbie. Also they will only help if you have one or two classes of boats they run. (Crackerboxes?). Otherwise you are the only guy with a <insert boat type here> and you are on your own!

So I have a vintage fiberglass flat bottom ski boat hull. And an O.S. .91 FSR marine conversion engine. I don’t want Mach 3 out of it, I just want to set it up to run, and run it for fun.

Q2) Recommended prop size/sizes?
Q3) Recommended Hardware setup? Straight shaft (what size?). Flex shaft (what size?). Outdrive/stinger from eBay (which one?).

Q4) Any other pitfalls or suggestions? It has been suggested I keep everything “under the hull”. Good advice? Bad? Neither? Any other hardware I should be trying to scrounge? Trim plates, turn fins, whatever?

Thank you for whatever help or advice you are willing to provide.

Paul
Cypress, CA
Sign up now
to remove ads between posts
Oct 28, 2019, 10:02 AM
Registered User
wparsons's Avatar
Not directly what you're asking for, but if you're just wanting to run for fun it might be way less headache to sell the nitro engine and convert it to a ~26cc gas engine.

For your actual questions, for a .91 you'll need a 1/4" flex shaft, no idea what size of prop or driveline setup to get. If you do run a fully submerged prop then you could run a straight shaft instead, and would need a smaller prop.

Any pictures of the hull?
Oct 29, 2019, 02:05 AM
GloBroz PowerLab
1QwkSport2.5r's Avatar
A 26cc has engine is going to have a whole lot more girth than an OS .91FSR, not to mention the power output will be similar with the OS having at least a few thousand more rpm worth of usable power.

Sorry, I am not much help on the OPs questions, but I would keep the OS .91 engine. The carburetor on that engine alone is worth more than the whole rest of the engine is!
Nov 01, 2019, 01:07 PM
Registered User
wparsons's Avatar
If it has standard width mounting rails in the hull, a 26cc will drop in no problem. Having run nitro boats a lot many years ago, as well as gas, gas is much better for sport running. Far less finicky, way less support equipment needed, way cheaper fuel. Depending on where the OP lives, finding proper boat nitro fuel might be an issue too.
Nov 02, 2019, 08:02 AM
GloBroz PowerLab
1QwkSport2.5r's Avatar
Quote:
Originally Posted by wparsons
If it has standard width mounting rails in the hull, a 26cc will drop in no problem. Having run nitro boats a lot many years ago, as well as gas, gas is much better for sport running. Far less finicky, way less support equipment needed, way cheaper fuel. Depending on where the OP lives, finding proper boat nitro fuel might be an issue too.
That .91FSR isn’t going to run regular boat fuel. It’s going to run best on low nitro airplane fuel. They run superbly on 0% nitro fuel too. All you need is 5-10% nitro - same fuel that was recommended for my mid ‘80s OS .21 SE-M. It ran poorly (really hot) on 20/20 fuel.

26cc gas is a bit bigger than a 15cc glow; I don’t recall off hand if the 91FSR is a big block like the 1.08FSR or if it’s in a 10cc case like the .61. If it is in a 1.08 case, it’s similar in physical size to the 26cc gas. BUT.... This gas versus glow argument has gotten really old.
Last edited by 1QwkSport2.5r; Nov 02, 2019 at 08:07 AM.
Nov 05, 2019, 12:27 PM
Registered User
wparsons's Avatar
You can't argue that gas isn't significantly easier for sport running... no glow igniter needed, no starter needed, way less tuning required, cheaper fuel, etc. You need a boat on a stand, the transmitter, and a jug of fuel.
Nov 19, 2019, 11:08 AM
Just a Balsa Building CL flyer
Thread OP

Hull pics...


And engine...

Still looking for advice.
Nov 20, 2019, 11:04 AM
Registered User
That's not an OS Max 91 FSR. It is an OS Max 91VRM, I didnt think OS made the 91 in a marine version, but only made a 65 and 81. It maybe a mix of parts from older versions of the 61/65/77/81/90 VRM, 91 VRDF (Ducted fan) and newer versions. Racers used to swap out the stock conrods for RPM rods. Run 12/15/20 percent nitro model airplane fuel with 20% oil and unless you really over rev it, the stock rod should be okay for sport running. Insane boats of SOCAL may have some parts you may want. I have found most newbe boaters, like you, experience sticker shock when buying new parts for thier flee market boat. It is possible to get parts on the cheap from nitro boating sites like - Intl Waters forum and going into the buy sell forum and placing a want ad. Sometimes older hardware that is just fine for sport running can be found with a classified ad. State of the art racing hardware is pricey and not really needed. Most boating retail sites only carry serious racing hardware and it's high price tag.
Last edited by Rudy F; Nov 20, 2019 at 11:09 AM.
Nov 20, 2019, 04:29 PM
Registered User
wparsons's Avatar
That hull looks a little small for an engine that size, especially since it's flat bottom and will plane easily. I think typically you'd want a .45 in a ~36" hull.
Nov 26, 2019, 07:00 AM
Registered User
ractsaf's Avatar
That Vintage OS Max 91 is to big for that Vintage Boat. Be good boat for .45 & on smooth water,on rough water,not so good. Good Luck!
Nov 26, 2019, 12:55 PM
///////
coriolan's Avatar
Quote:
Originally Posted by wparsons
That hull looks a little small for an engine that size, especially since it's flat bottom and will plane easily. I think typically you'd want a .45 in a ~36" hull.
During the 80's one club member shoehorned a 15cc ROSSI into a Class-A mono hull (Prather)and launched it for a glorious run.....It rolled over as soon as the engine came on pipe


Quick Reply
Message:

Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion Newbie with old Heli needs help ID-ing KillerRabbit Fuel Heli Talk 8 Dec 16, 2017 10:21 PM
Help! Old newbie with advancing senility needs help! JerEl Multirotor Drone Electronics 3 Dec 04, 2016 06:09 AM
Discussion OS 90 FSR Vs, 91 FSR ? N99JH Engines 20 Oct 23, 2015 06:56 PM
Discussion Need muffler help w/.60 size top flite P-51D and OS.91 FSR sstewart1 Fuel Warbirds 1 May 03, 2010 05:25 PM
Discussion Need Help in parameters of 0.91-FX OS saadlahori Fuel Plane Talk 5 Jan 21, 2009 02:45 PM