8 or 9.9 hp

[Rranger]

I have a 21 foot Fibreform with a flying bridge. Looking to switch my kicker and wondered if a 8 hp would do it. 9.9's seem to be the norm, is there that much of a drop off that the 8 hp wouldn't do the job. In rough water I'd be using the inboard. Thanks for input.

 

[gm280]

Rranger, I once had a 7.5HP Ted Williams OB engine and it worked very well on my little 12 foot boat. But when I bought a new Mercury 9.8HP it was night and day difference. But of course we are talking an air cooled 7.5 Ted Williams to a new 9.8 Mercury as well. However, I honestly don't think you would see a huge difference between an 8HP and a 9.9HP OB myself. But that is just my opinion!

 

[Sea Rider]

Which OB brand are we talking about ? If 2 strokes Merc, Tohatsu, Nissan a 9.8 is just 170 CC compaed to a 250 CC of a 9.9/15 HP. For a kicker you need pushing power specially on wavy, windy conditions if main engine fails. Much better for a prop maximization than an 8 HP.

Happy Boating

 

[ondarvr]

There will be a difference, and buying a high thrust model will be much better. A high thrust 8 will perform much better than a normal 9.9

 

[Sea Rider]

A high trust OB comes factory delivered with 4 blade prop, available on the 4 strokes Sail 6 HP-SP model, counting with + 70 CC more of the 9.8 model makes a world of difference, buy a 2 or 4 strokes 9.8 OB and optimize the prop performance with a 4 blade, will need a induction tach to check that OB runs inside safe wot rpm range.

Happy Boating

 

[ondarvr]

Adding a high thrust prop to a normal motor doesn't get you to the place as a high thrust motor, there's big difference between the two.

 

[Sea Rider]

OP has not specifed brand model, so will be wild guessing, assuming. If you add a 4 blade prop to the same standard portable model OB, will have a High Trrust OB, due to both having same gear ratio, same lower gear case, including same wot rpm range, It's same OB with different shoes. One has track shoes, the other tennis shoes on same field scenario.

High Trust OB are mainly used for powering heavy boats as sailboats, won't be possible to plane, will be pushed much better achieving better fast displacement speeds than same standard model due to having one more blade to grip better on water. Most boaters assumes that by placing a High Trust OB is winning the lotto, All portable OB's used as aux should be tached to check if working inside factory wot range, preferably at the max side of the wot range if pushing heavy boats.

Happy Boating

 

[Rranger]

Which OB brand are we talking about ? If 2 strokes Merc, Tohatsu, Nissan a 9.8 is just 170 CC compaed to a 250 CC of a 9.9/15 HP. For a kicker you need pushing power specially on wavy, windy conditions if main engine fails. Much better for a prop maximization than an 8 HP.

Happy Boating

​So would a 8 hp high thrust push my 21foot around for trolling purposes only in calm waters. I fish inland only and if water is rough I troll with inboard.

 

[ondarvr]

A true high thrust model will do it easily, just putting a high thrust prop on a regular motor will make it better than with the normal prop, but not as good as a true high thrust motor.

The high thrust motors have a larger gear case and lower ratio, so they can run larger props that get a better bite.

A normal 8hp would move it ok in most conditions.

 

[Rranger]

A true high thrust model will do it easily, just putting a high thrust prop on a regular motor will make it better than with the normal prop, but not as good as a true high thrust motor.




The high thrust motors have a larger gear case and lower ratio, so they can run larger props that get a better bite.

A normal 8hp would move it ok in most conditions.

So I have this clear a normal 8hp should move my 21 ft flying bridge in normal water and a 8 hp would be more efficient by the sounds of it .

 

[ondarvr]

Yes, a normal 8 will OK, you can upgrade from there depending what motors are available to you when you're ready to buy. Then if it's a normal motor put a high thrust prop on it for better results.

 

[Sea Rider]

Quote : So I have this clear a normal 8hp should move my 21 ft flying bridge in normal water and a 8 hp would be more efficient by the sounds of it . There seems to be a typo error....

Which brand are we talking about, 2 or 4 strokes OB ? Was the original post 8 or 9.8 HP ? Now see 8 or 9.9. A 9.9 which is a 250 CC OB has nothing to do with an 8 or 9.8 HP OB, it's a different animal.

Which "portable High Trust" brand comes with bigger gear case as opposed to same standard model, say 8-9.8-9.9 HP ? bigger gear case are usually available on much larger OB for commercial use.

Your 8 HP OB will need a prop maximization to rev near max wor rpm for your application, need to install an induction tach to check wot revs lightly loaded and compare them to their factory wot range. Once best prop is dialed you can rev your engine at any rpm you like with no issues.

Happy Boating

 

[Rranger]

Quote : So I have this clear a normal 8hp should move my 21 ft flying bridge in normal water and a 8 hp would be more efficient by the sounds of it . There seems to be a typo error....






Which brand are we talking about, 2 or 4 strokes OB ? Was the original post 8 or 9.8 HP ? Now see 8 or 9.9. A 9.9 which is a 250 CC OB has nothing to do with an 8 or 9.8 HP OB, it's a different animal.

Which "portable High Trust" brand comes with bigger gear case as opposed to same standard model, say 8-9.8-9.9 HP ? bigger gear case are usually available on much larger OB for commercial use.

Your 8 HP OB will need a prop maximization to rev near max wor rpm for your application, need to install an induction tach to check wot revs lightly loaded and compare them to their factory wot range. Once best prop is dialed you can rev your engine at any rpm you like with no issues.

Happy Boating

Talking a "normal " four stroke 8hp or a 4 stroke 8 hp high thrust. Will either one push my 21 foot Fibreform with a flying bridge for normal trolling on inland waters?. Is there such a thing as 2 stroke high thrust?
And from what I've heard putting high thrust props on "normal" four stroke's is not a good idea.

 

[ondarvr]

Let's see, which brands come with a bigger gearcase in the portable range.

Yamaha, Honda and Mercury, there are probably others.

There are larger models too, some called high thrust, and others were marketed as commercial models.

 

[ondarvr]

Talking a "normal " four stroke 8hp or a 4 stroke 8 hp high thrust. Will either one push my 21 foot Fibreform with a flying bridge for normal trolling on inland waters?. Is there such a thing as 2 stroke high thrust?
And from what I've heard putting high thrust props on "normal" four stroke's is not a good idea.

I don't know of any 2 stroke high thrust kickers, but there may have been some in the past. It's not a problem putting a high thrust prop on a small 4 stroke.

 

[Sea Rider]

Which 8 HP High Trust OB brand have you found so far or know about. Just to check specs. Still don't buy it, why would you need a larger gear case on a 8 HP OB when you can get same performance with a 4 blade or better performance with less 3 blade on same standard OB...

Happy Boating

 

[ondarvr]

Which 8 HP High Trust OB brand have you found so far or know about. Just to check specs. Still don't buy it, why would you need a larger gear case on a 8 HP OB when you can get same performance with a 4 blade or better performance with less 3 blade on same standard OB...

Happy Boating

I don't mean this as slam, but by saying this it's obvious you don't know anything about small outboards other than Tohatsu, nor do you know anything about high thrust kickers.

Yamaha made a T8 until just a few years ago, it was a great high thrust kicker, and yes, it had the larger gearcase so it could run the much larger high thrust prop. It was a best seller in markets that used kickers, but since they also had a T9.9 they dropped the smaller model because there was too much overlap in the market with two in that size range.

If you think putting a high thrust prop on a regular kicker makes it the same as a high thrust model then you have much to learn.

 

[Sea Rider]

Sorry Ondarvr, this was a OP question, if someone asks for advice here should post complete information. OTOH why do you like to post old irrelevant information, come on we?re in 2016, leave the past in the past. Useless info for OP or any other searching same...

Happy Boating

 

[fishin98]

This past summer I purchased a 1999 Merc 15hp 2str, that came off the back of a sailboat. It has a 6.5P prop on it. I would think either the 8 or 9.9 would be fine. If you need a bit more thrust, look at a different prop with a lower pitch. On my 2000 Bayliner 1802 Capri Cuddy, I used a 2007 MERC 5HP 4STR kicker for trolling for walleyes on Center Hill and Dale Hollow lakes in TN, did a fine job.

 

[ondarvr]

The T 8 was around for a very long time, there are still a bunch of them out there, even new stock shows up, it's not an a old style motor. It was just recently dropped. And I don't think the OP ever indicated if he was going to buy new or used.

I understand completely why someone should look for a high thrust motor, even if they don't know they exist when they ask the kicker question they should be told about them. If someone is going to buy a kicker for a boat that size their first choice should be high thrust if possible, adding a high thrust prop to a normal motor helps, but only gets you about 1/3 of the way there.