InBoard vs OutBoard?

[QC]

Re: InBoard vs OutBoard?

ewen,<br /><br />trog is right. Horsepower is horsepower. The extra RPM from the outboard is meaningless unless you know the gear ratio. You CANNOT spin that prop faster without MORE bhp. Period. Do not get hung up on the higher RPM as again the prop speed is determined by RPM * gear ratio. Prop speed is what we care about here, not engine RPM. If your understanding was correct we would all run Cox airplane engines: horsepower doesn't matter all we need is RPM . . .<br /><br />rodbolt,<br /><br />You're missing that the comparison was between an I/O gasser an I/O diesel and the OB. There is no inboard in the test. So the under hull stuff doen't come into play. I totally agree with your copmparisons of a true inboard though. Believe it or not trog is on it this time. Either the outboard produces more power or the I/Os are sick. Personally I believe the outboard produces more power than advertised. Your fulcrum example comes into play too, but not 8 MPH's worth . . .

 

[QC]

Re: InBoard vs OutBoard?

ooops: double post

 

[DeliveryCaptain]

Re: InBoard vs OutBoard?

I think the Initial Question got Lost// He needed an acurate comparison for IO versus the Outboard.. Yes the O.B. is a bit more Expensive, BUT where he is boating in Biscayne Bay, ICW, or just up the Atlantic to Port Everglades..IO can do the JOB. WITH StingRay for Exp. a 195LR w/4.3 SIX-195hp. is about equivalent to 200-4stroke Yamaha/SUzuki? Merc-Verado?? It will do steady 44mph/ and WOT is over 53.2mph!! come-on in a similiar 19' or 20' with 200hp. you might go 57 or 56 topend? BUT difference in Motor cost is Nearly 20% higher/ F200 Yamaha is $15890./ a 195 V-6 Mercruiser is ONLY $12700. for the EXTRA $3200.?? come ON/ gives this guy the OPTIONS/ Just a boat captain's perspective on Many Boats moved here in S. FLorida. Hope this DATA! HELPS you, INTI> A little Knowledge, is sometimes a Dangerous Thing>

 

[ewenm]

Re: InBoard vs OutBoard?

hey Rodbolt<br />thats typical of what i mean about service - with moored boats there is an added responsibility to check the thing. I typically check my boat twice a week have a look at mooring lines check bilges pumps and float switches. and when ever we use it, more so in the warmer months i take some time to wipe down the hull and clean around the leg particularly around the bellows just for the reasons you state, that barnicles can wreck your day.and typically haul it twice a year to antifoul the leg and detail it. my point is that, that is the minimum that one should do and it should be considered as part of boat ownership.and the type of power you chose to run will have its own special needs there is no free lunch with boats<br /><br />for new boat owners this and other web sites have a wealth of knowledge but also a lot of c@@p to sift through, and making blanket statements about power options is not helpful for newcomers<br /><br />Quitecat i think you fail to appreciate the reality of gearing look at the current crop of small engined turbo cars and compare with a typical V8, my 94 cherokee is a classic example of truck loads of bottom end grunt up to about 4000 rpm and then compare with my similar weight non turbo mazda 6 a lot less hp and torque but revs to 6500 rpm and above 3500 it eats the jeep same with outboards they typically run less pitch which alows them to keep up with the i/o down low but run harder at the top end because of less pitch and different gearing<br /><br />and its a week day and every weekend lately has been to windy for boating so iv got the mega sh#ts so dont start me up<br /><br />Best regards From Australia<br />Ewen

 

[Solittle]

Re: InBoard vs OutBoard?

Inti - You said "I'll primarily be using the boat in saltwater on the weekends w/ wife and family, for snorkeling, diving, etc.."<br /><br />I have been doing just that for the past 35 years out of Miami. Last Friday I took my wife and two daughters down to John Penneycamp park in Key Largo for an afternoon of snorkeling. It doesn't get any better.<br /><br />Give some thought to getting something a tad bigger than 17-18'. You will be greatly limiting when you can go out and where due to wind & waves. It is no fun to be out pounding across Biscayne Bay in a boat that small and I have done it for years.<br /><br />I offer two suggestions. The smaller of the two rigs would be a 20'er with a single V6 outboard on the back - used of course. The center console (CC) is the most flexible for what you intend to do - - and you don't have to be a fisherman. My first choice would be along with what I have now which is a 23' CC with twin outboard engines. V6s if speed is important but V4s will do just fine. My rig is a 1988 Wellcraft CC with twin 1.6L V4s.<br /><br />Before you dive in spend a pile of dough spend few hours on a Saturday or Sunday at the Matheson Hammock and Black Point marinas and talk to folks who have boats that interest you.<br /><br />Don't forget to give some though to your tow vehicle.

 

[QC]

Re: InBoard vs OutBoard?

Originally posted by ewen:<br /> Quitecat i think you fail to appreciate the reality of gearing look at the current crop of small engined turbo cars and compare with a typical V8, my 94 cherokee is a classic example of truck loads of bottom end grunt up to about 4000 rpm and then compare with my similar weight non turbo mazda 6 a lot less hp and torque but revs to 6500 rpm and above 3500 it eats the jeep same with outboards they typically run less pitch which alows them to keep up with the i/o down low but run harder at the top end because of less pitch and different gearing<br />

Dude, like wow, I have been in the heavy truck business for 27 years. I sell horsepower and make gearing recommendations every day. I promise you that I understand horsepower, torque, gearing etc. to a degree that you should trust. You, frankly are failing to understand that horsepower IS horsepower. What you do with gearing is that you change the output speed of the device that delivers that horsepower (driveshaft, propshaft etc.), not the actual horsepower. Horsepower equals work, work equals speed against a given load. Period. End of story. Your Mazda and Jeep example prove this, they don't disprove it.<br /><br />Sorry for the rant, but this happens to be my favorite topic and your understanding is one of the most common misconceptions. Stare at this calc. It is the whole story. bhp=torque*RPM/5252<br /><br />So in the case of your Mazda, it has less torque but way more RPM , so it makes similar bhp. I have no specs and am basing this on your note, but there is no way that a Jeep Cherokee and a Mazda 6 have equal weight, and their respective aerodynamics are very different. Gearing can definitely affect performance at different speeds and acceleration, but it does nothing to the amount of work "available" from given horsepower. Whether you make 350 bhp at 1800 RPM (like some heavy diesels) or 350 at 10,000 RPM like a really tweaked small displacement race engine of some type, it is still 350 bhp. The difference is only the output speed of the crankshaft, which has to be made useable by gearing. If you set these two different engines up to lift a load (like a crane) and they were geared so that the speed of the winch was the same speed, then they would theoretically lift the same load to the same height at the same speed. That is horsepower. In the case of the marine engine, yes, that different speed will require different gearing and/or a different propeller, but the work available at WOT RPM is the same.<br /><br />Soooooo, the 135 bhp OB should not be able to get 8 MPH more than the 135 bhp I/O which are both rated at the propshaft unless one is incorrectly rated, or one is sick, or one combo weighs a very different amount. The article answers the weight, the ratings are what are advertised, so the most likely assumption that can be made is that the actual bhp is different than the advertised, one is either sick or better than advertised. Other possibilities are a problem with the hull or rodbolt's fulcrum deal. Frankly, I agree with rodbolt, but not 8 MPH worth of agreement. <br /><br />Good on ya mate.

 

[Lou C]

Re: InBoard vs OutBoard?

Another question with marine engines is that we never (or just about never) are given a torque rating, which is always a very significant # with cars/trucks. Given = weight and hp, the engine with more torque will accelerate the vehicle faster at low speeds, it is a very noticable difference in the feel of the vehicle. We hear that inboards/i/os have more torque but maybe this is offset by the weight difference. It is hard to imagine that a 2.5 liter OB puts out as much toque as a 4.3 I/O but the #s don't lie I guess.

 

[QC]

Re: InBoard vs OutBoard?

Lou,<br /><br />You are right, the OB does not put out the same torque, that's why it must spin faster to make the same bhp The reason that marine manufacturers don't put out torque numbers is that it is less significant than in a vehilce. Good low end torque helps a marine engine get on plane a little faster, but the fact is that porpeller load curves are basically linear, so the low RPM torque capabilities of the engine are rarely in the equation. Most of those same manufacturers show a prop load curve on their sites. If you go back to the bhp=torque*rpm/5252 thing and stare at those prop "curves" it should make more sense.

 

[ewenm]

Re: InBoard vs OutBoard?

Quietcat <br /><br />thanks for your insite, i checked the specs for my jeep 175hp, 222fp torque 3406lb and mazda 163hp, 152fp and 3159lb so yeah the jeep is slightly heavier but the hp and torque are higher (plus those numbers are factory and this vehicle has 10 years work on it)and it has the aerodynamics of a brick but the mazda for all its advantages is vastly and dramatically faster.<br /><br />interesting comments about the prop and its power delivery curve ive not considered that, and while i accept what you are saying about hp there is no denying how much faster 2 stroke outboards are than the same hp i/o 4 stroke. and buy the way i personally would never chose anything but a i/o or shaft drive for me its because i feel comfortable with a 4 cycle car type engine<br /><br />Ewen

 

[QC]

Re: InBoard vs OutBoard?

ewen,<br /><br />Yeah wheeled vehicles are an interesting challenge as gearing DOES matter as what makes the difference is the bhp applied to the road, so the RPM x the individual gear ratio (1,2,3,4 or 5)x the final drive ratio x the tire size result in torque (and of course coupled to RPM which gets us the bhp) to the road. When you consider also that the tires on the Jeep have higher rolling resistance along with the weight and maybe even fewer gears, then yes you will see differences in performance.<br /><br />This sounds a little like a reversal, but you have to remember a major issue. The marine engines, if properly propped, are operating at max bhp at WOT. This is an area that you rarely operate your cars: basically the only consistent way to do it is to go as fast as possible and select the gear that makes it go the fastest (sometimes 4th not 5th . . .). Sooooo, although I agree that Outboards are often faster than their I/O counterparts it is usally because they are lighter (in the test example they weren't, but older V6 outboards were less than 400 lbs, where as I/O's run 700 - 1000 lbs) AND because until 10 - 15 years ago OBs were rated at the propshaft and I/Os were rated at the flywheel which is about a 25 bhp penalty on the I/O AND because Outboards are more adjustable on the boat; X dimension height and trim differences favor the OB. Fun discussion!!

 

[rodbolt]

Re: InBoard vs OutBoard?

quietcat<br /> ya still forgot that hp makes it go and torque helps it keep going. if ya dont belive it next time your checking the rolling torque on a drive look how the needle jumps during break away and settles while your rotating it. the torque curve on a two stroke is more linear with RPM than a 4 stroke. the crankshaft is nothing more than a set of levers.<br /> apply thrust on the lever and it makes horespower and torque.<br /> a four stroke applies thrust everyother time the lever is in position and every other time frictional losses eat power and torque, a two stroke on the other hand gives a power impulse every time the lever is in position and makes the curves a lot higher. the disadvantage is more fuel is required. more heat is generated that MUST be dissapated. but the topic was inboard to outboard. my 19ft thunder chicken with a 120 85 model jonnyrude can keep up with the 325HP seamax in the towboat. tow boat is a 20ft shamrock. he is turning 4100 and I am turning 5300. both of us are at or near max. mine has a lot less drag in the water and 1/2 the wetted hull surface. he is burning about 6 gallons an hour and I am burning about 10. but from Manteo to collington,about 8 miles, we will idle in the channel together.<br /> so when it comes to 2 sroke or 4 ya just cannot go HP to HP.<br /> it wont work. even when we change out a 150 2 stroke to a 150 four stroke we normally lose a bit of top end. I have dynoed to many to say that two strokes are underated.<br /> not to say that occasionally someone will . suzuki,yamaha and merc have all been busted for it by the NMMA and BIA.<br /> its like my old inline six 150 merc. I think it was rated at 5000 rpm. but it would turn 6000 all day long if trimmed and propped right. my 17 cajun would go a bit faster at 6K with a slightly smaller prop than 5K with a bigger one.

 

[QC]

Re: InBoard vs OutBoard?

rodbolt,<br /><br />I agree. Towboats waste a lot of bhp. On your repowers, aren't all of the 4 strokers heavier than the 2 strokers? Wouldn't that account for some of the loss in speed? Maybe the 2 stroker will maintain the bhp higher, but if it is makin' more bhp up there then it is makin' more bhp. Right?<br /><br />Also, you're right the original topic was inboard to outboard, but he meant I/O . . . There have been two article links posted recently (one above) that was supposed to solve some of this debate, but all they did was confuse it IMHO. I don't care if it is a steam engine or a turbine, if you are harnessing the bhp off of a shaft, bhp is relevant, important and ultimately what determines the speed of whatever you are moving with that shaft. And if you change the speed at that shaft with gearing, the bhp stays the same with the exception of any lost through the gearing mechanism. If you slow it down, torque goes up, but the combo of speed and torque results in the same bhp. If you speed it up, torque drops and RPM has gone up resulting in the same bhp out the shaft. Some will say "wait the slower shaft moved the load a shorter distance". They would be right, but the combo could lift a heavier load that shorter distance, so again the work (bhp) available from the shaft is the same.<br /><br />When you add propellers, trim and X dimension into the mix then it gets a little (a lot) screwy. I would still submit, if you could instantaneously swap an equally weighted four stroker (or anything else for that matter) onto your boat with the old merc and also instantaneously change the gear ratio so that the prop shaft was spinning the same speed, that the boat would go the same speed. The example of your merc going from 5000 RPM to 6000 RPM is fun because it challenges all of this, but the propeller thing is the key. If that prop was slightly more efficient that could explain some of it, but I submit that the 6000 RPM x the torque at that speed resulted in slightly more bhp at the propshaft. Whatever the advertised bhp rating or advertised rated RPM was. I am, however, beginning to see the point that a two stroker is more variable as compared to the manufacturer recommendations and ratings.<br /><br />I hope you see this as fun. Upinsmoke and I had a similar debate in a towing thread. Personal experience often seems to contradict the mathematics, but I believe the math is always valid, just a little hidden sometimes under combustion, gearing, propellers, trim etc. Especially true with boats as the hull brings in even more variables.

 

[dingbat]

Re: InBoard vs OutBoard?

Quietcat<br />All of you're argument is based upon a load being in equilibrium with the available Torque. If you have more Torque available than is required to move the load at a given speed then throwing more HP on the input shaft of the gearbox doesn’t buy you any more speed. At this point you’re being limited to the speed of the output shaft of the motor not the HP on the output.

 

[DeliveryCaptain]

Re: InBoard vs OutBoard?

This Poor Guy just wanted a comparative FOR: OB versus the IO> I still contend that in a 20'CC OB v. a 195 Bowrider with a 195 4.3 V-6 would do him just as well FOR A LOT LESS $$ Sorry, I have been selling or Moving them since 1982/ It is Just the RAW DATA AND> I sell both CC's and Bow thumpers** Have owned FOUR SeaCrafts ALL with OB's so I believe gives some Credibility for a fair and Unbiased Opinion. And as for Boating in Biscayne Bay, It is usually, 2-3ft. seas and Any 19 or 20footer can Handle it!! Just a few more comments from S. FLA capt. Good Luck with his Purchase/

 

[QC]

Re: InBoard vs OutBoard?

Originally posted by dingbat:<br />If you have more Torque available than is required to move the load at a given speed then throwing more HP on the input shaft of the gearbox doesn’t buy you any more speed.

What? You can't "throw" more bhp on the shaft without using more of the available torque or increasing the speed . . . If you have more torque available at ANY speed, then you have the ability to make more horsepower. This is why I spend time on this discussion. People always try to seperate torque and horsepower. You can't unless you are torquing main bolts at about, oh, let's say 1/1000 of 1 RPM, which is actually still bhp. Torque + speed of that torque equals bhp. Many think torque alone is important, it is for breaking a load free (like the first crack at the main bolt), but it won't keep it moving with out RPM.

 

[Inti]

Re: InBoard vs OutBoard?

yeah, your the one I need to talk to!!<br />I agree w/ the bigger the better concept, but I'm limited on my towing vehicle! And I cant afford to upgrade vehicle and get a boat, its one or the other for me <br />My family has a place in Matecumbe Key so I'll be dropping in out of that area, I dont really have to deal w/ Biscayne Bay and Govt Cut!!<br />Thanx for the info though.<br /><br />Also can you recomend any other places to dive/snorkle worth going to, email me inti27@gmail.com<br /><br />Thanx again, soLittle!<br /><br />

Originally posted by SoLittle:<br /> Inti - You said "I'll primarily be using the boat in saltwater on the weekends w/ wife and family, for snorkeling, diving, etc.."<br /><br />I have been doing just that for the past 35 years out of Miami. Last Friday I took my wife and two daughters down to John Penneycamp park in Key Largo for an afternoon of snorkeling. It doesn't get any better.<br /><br />Give some thought to getting something a tad bigger than 17-18'. You will be greatly limiting when you can go out and where due to wind & waves. It is no fun to be out pounding across Biscayne Bay in a boat that small and I have done it for years.<br /><br />I offer two suggestions. The smaller of the two rigs would be a 20'er with a single V6 outboard on the back - used of course. The center console (CC) is the most flexible for what you intend to do - - and you don't have to be a fisherman. My first choice would be along with what I have now which is a 23' CC with twin outboard engines. V6s if speed is important but V4s will do just fine. My rig is a 1988 Wellcraft CC with twin 1.6L V4s.<br /><br />Before you dive in spend a pile of dough spend few hours on a Saturday or Sunday at the Matheson Hammock and Black Point marinas and talk to folks who have boats that interest you.<br /><br />Don't forget to give some though to your tow vehicle.

 

[ewenm]

Re: InBoard vs OutBoard?

getting back to the original post, not that this hasent been fun AND informative, what can be said is different power methods suit different applications and you best try before you buy. direct comparisons of different power on the same hull are inconclusive due to the different characteristics of each power option, EXCEPT for two things dont settle for minimum power and ask around for the different costs and needs of the power options available and then decide which you can comfortably afford.because the quickest way to lose interest in boats is to minimize the ongoing cost of service, many consider that 10% of the purchase price should be allowed for annual service costs another is that the purchase price is just the deposit<br /><br />but when your out on the water all the above seem to fade away<br /><br />Ewen

 

[QC]

Re: InBoard vs OutBoard?

Inti,<br /><br />Sorry for the thread hi-jack . . .<br /><br />I just read your thread over on towing that was about your vehicle. I think the weight discussion makes up your mind. Outboard Center Console. 17 ft. max probably. The CC for the activities you plan, outboard for the weight savings. In that size boat the weight difference will be substantial. Everything else we have talked about over here is waaaaazy too heavy.<br /><br />Take a look at this<br /><br /> http://www.triumphboats.com/boats/170cc.htm <br /><br />or this<br /><br /> http://www.bostonwhaler.com/Rec/default.asp?content=boats&family=legend&number=170&type=Montauk <br /><br />As SoLittle said these will be less flexible in regards to the weather, but your truck is the limiting factor. What's your budget? Good luck!! Wish I was going shopping with you, lots of fun!!!

 

[yater]

Re: InBoard vs OutBoard?

I just sold my '76 correct craft ski tique (ford 302) and all I can say is NEVER AGAIN will I own an american v-8. That thing nickel and dimed me to death. I was trying to hold back the cheering as the guy took off with it. It was one thing after another with that damn motor. I would have kept the boat if I could find a toyota or nissan V-8 to cram in it.

 

[Inti]

Re: InBoard vs OutBoard?

Hey Quietcat, I agree thats what Im shooting for 17'. My budget is around 20 - 25k, depending on the boat and the wife <br />Have you heard of Key West, Scout or Mckee boats??<br />Are they good, bad?<br />Thanx again, <br /><br />Inti