nickrummy

Can anyone help me identify this boat? Are the motors worth anything? Has tons of compression and feels smooth. Measures 45" tip of bow to transom.

Album here

Dan S

Don't know the boat but the engine is a K&B 7.5cc (.45) maybe an 11cc, need to see the other side of the engine.

Dan.

nickrummy

I was told it's a .40, on the other side it says 7.5 so I am assuming that's the 7.5cc

Ron Olson

My Feedback: (1)

It might be a Dumas Scarab but not 100% sure. The engine really needs to be raised though. It's about an inch or more too low.

scardina

My Feedback: (3)

7.5 translates to .457, usually just considered a .45 or a .46 from what i know, the K&B engines are all pretty good, i've personally got a 7.5 inboard and a 3.5 outboard (.21) and they both have got plenty of go, and only running 30% at the moment.

quite an odd thing to see an outboard on a mono, theyre usually reserved for tunnels and not much of anything else. i had heard about attempts at putting them on monos some time ago, but it didnt work too well so they gave up on the idea, lol.

nickrummy

Any reason why they aren't that common on the monos? I figured I'll go through the motor to see what shape it's in and try to at least fire it up.

TCHedOff

I read a thread somewhere where a guy claimed he started the trend of running outboards on mono's 20 some yrs ago and he stated he was sad to see them become a dying breed. Back then K&B outboards dominated the engine market and there were less mfrs to choose from. Since then, inboards have become plentiful, better made (materials & design), and more powerful while K&B remained relatively unchanged. This has lead to their decline - people want the hottest and fastest setups.... hence you dont see K&B's outboards on mono's anymore. But your boat should work fine for having fun and driving. BTW: Ron O has a TON of mono experience - if he says raise the engine an inch, it is worth doing.

nickrummy

I wondered why it was so low too. My first question was isn't the head going to be really close to the water line? Is there a reference point I can use to make it the right height?

Is the boat runnable right now or should I move the motor up first? I'd like to see if it will run. All the linkages are already setup I just need to add servos. If I need to move the motor up then I'll have to move all the linkages and holes in the transom up also. Can I just patch the holes with some epoxy?

TCHedOff

Im not qualified to answer about a reference point to try starting at 'cept for Ron's pointer. As for running it as is, why not - you got that way so why not try it? And Yes, epoxy will seal the holes just fine.

Ron Olson

My Feedback: (1)

Usually as a reference for outboards people seem to use the centerline of the propshaft when setting them up. On a Vee hulled boat I'd start it with the propshaft just under the bottom of the Vee then adjust it from there.
The job shouldn't be that hard to do except for the throttle linkage but still shouldn't be a big deal. The engine can be raised then use the lower set of engine lugs to mount the steering arm to and possibly flip the ball connectors over to the bottom side. Of course you're going to have to fill the old holes in the transom.

I don't have a lot of experience with OB monos but mostly with OB tunnel boats. I did sell a hull to a buddy that had been sitting untouched in my basement for years that he dropped an OS .21 OB on. It really didn't do too bad once we did a little tweaking on it.

nickrummy

Thanks Ron, I looked at the photos and see what you mean about steering linkages. That's an easy fix. Hopefully I can come up with something for the throttle without having to remove the pass through in the transom.

Is it ok for the exhaust to be that low in the water if I want to make a couple test passes the way it sits now? I'd imagine on plain there won't be much of the boat in the water?

I have a '65 18' Thompson with a Merc outboard so I have a decent knowledge of how boats work. Just not in this scale!

Ron Olson

My Feedback: (1)

You can try it as is but when changed you'll see a good 5-10 MPH gain.
Full-sized boat experience sure does help as it makes things easier to see and understand in the model boating world. Look at your Thompson and see where things match up as far as engine height goes.

jac32224

Nickrummy... Here is a boat I built 15-18 years ago. One of those things... Had the hull... Had the engine and figured why not. An outboard mono is a tricky beast. Granted mine is WAY overpowered. I built it as a "FUN" boat, never intended to race, and it is a lot of fun. If you do move the engine up, which I think you'll have to, get an adjustable mount so you can adjust the height, and play with the engine angle a bit too. If you notice, my engine is all the way up on the mount, and I wish I could raise it a bit more. Weight has beenan issue for me as well. Adding weight to the bow has really improved how it handles. My radio box is forward and my tank is in the rear, which made the cables much straighter. Hope that helps a little... Just my 2 cents. I am NOT an expert with this set up, just passing on my personal experience.

nickrummy

Very awesome Jac! What hurts the performance running the outboard? Weight distribution? The way the whole assembly pivots for steering instead of just using a rudder? I definitely won't be racing. This hobby is all about fun and learning to me. Just branching off a bit with this new to me side of RC.

Do those trim tabs work as well as they do on the 1:1 boats? Luckily I have a LHS close to me that deals with boats. I used to never go there since all he had was boats and planes but now I have a reason go in and BS with him.

I see most nitros aren't running an air cleaner? I'd imagine there isn't much dust out on the water but what about spray? Do people just put a plug over the carb while transporting or in storage?

jac32224

Honestly... I feel its the hull setup. OB's work great on tunnels. I went with large tabs for two reasons. One, was for ride adjustment, but mostly to keep it from hooking in the turns. Again, I don't race, so I don't always make a nice sweeping turn. My thought, and I could be wrong about this, with an OB on a V hull the prop is pretty far back, plus since the prop pivits, it pushs the hull through the turn much differently. It seems to want to roll the hull on its side. You'll find that you need far less steering throw from your servo than you may think. The large tabs on the rear do help control that roll. That was my theory anyway...LOL

Compaired to inboards, the weight is far more rearward. Most (if not all) V hulls are set up for inboards. To me it just makes sense that you have to compensate somehow for that weight shift. The tabs can help force it over a bit, but its really just fighting itself at that point. Again, I highly recomend the adjustable mount. Make a run... then change it a bit. It may get better... or worse, but you'll have the ability to do so quickly, without drilling and filling over and over.

Yes... I just use a rubber cap over the carb when not in use.

nickrummy

What about using more severe rails on the bottom of the hull (Sorry not sure what the terminology is) Also the center rail doesn't seem that drastic? That usually keeps the tracking in the water straight doesn't it?

I know when you make a turn with the OB the natural thrust direction change makes the lower unit of the motor want to almost roll under the boat causing the inner side of the boat to drop in the turn. It makes it want to barrel roll almost (extreme example but thats the motion I'm getting at) On an IB the thrust stays horizontal and the rutter just changes steering direction instead of trying to roll the boat.

I know this isn't RC related but it's a photo I took my T&T and it shows that roll under pretty well I think. (I'm sure you guys know about this, I'm just babbling haha)

jac32224

I've been around boats (full scale) most of my life... I've done 130mph in the cat below, and done a lot of fishing offshore in big outboard fishing boats as well... I think the true problem is, models share the same basic theories, but they are never truly to scale. Example... Your outboard (7.5) puts out what? 1hp? probably more, but your model weighs 5 pounds. What if your real boat had 1hp per every 5 pounds of weight? See my point? If things were to scale... Your typical 1/8 scale racing cat would do 20mph or so... Whats the fun in that!

nickrummy

Good point Jac. Boy what I would do to get a ride in one those boats!

jac32224

Ride... Yes. Pay for fuel... NO WAY. My buddy owned the yellow Hyrda-Sport. He sold it a year ago. We were chatting the other day about the boat. Figured running it hard at todays fuel and oil prices (has 3 250 yamaha 2-strokes) it would honestly cost five dollars a minute to run. Burns 65 gallons an hour at 58mph, plus oil. Last I heard Yama-lube oil was 25 a gallon...

nickrummy

No doubt. My boat isn't really a gas guzzler but by the time I haul it out to the lake and go out on the water for the day $$$

One thing better than owning a boat, and that's knowing someone that owns a boat!

jac32224

Nick... Shoot me a PM if you want and I'll pass on my personal email. Again... I'm no expert, but I may be able to help a little... John

nickrummy

It says you have your permissions set not to accept PMs

ryan_t888

A 7.5cc engine on a 45" mono will be slow! That's a lot of hull for little power. Typically you would see the 11cc or 13cc engine on something of this size.

BTW, the K&B 7.5cc stock will be one of the loudest rc model engines you will hear.

Ryan

jac32224

Nick... Try again. Just checked settings and its fine. Plus received one today prior to reading your response... Don't know why, but please try again

nickrummy

Well it fired up so that is good news! It needed a new glow plug and I need to replace the tank but at least it runs.

Here is a video of the test fire. Didn't let it run long so there was obviously no cooling.

http://vimeo.com/1680754