Can a 170 safely support a 4 stroke?

[Flapilot]

I'm in the process of checking out a 170 that has a Honda 90hp 4 stroke on the back of it.  Would structural changes needed to have been made when they did the rebuild to accommodate the weight?  Is there any way to check if those changes were accomplished?

I'm going to sea trial the boat to make sure it's not causing wet floors as well. Any suggestions beyond that?

[RickK]

Welcome aboard Flapilot. 
What year is the boat (170 was from '69 until they changed the decals to 175 in the late 80s) and what year is the Honda? 
The Honda is heavier than a 2 stroke Johnson, for example, by anywhere from 40-100 lbs depending on the year, so you can expect that walking to the back of the boat will cause water to come in through the scuppers.
If the boat was rebuilt, they could have moved the fuel tank forward, although there isn't a tone of room in a 170, or they could move the console forward.  You could tell if the console is moved forward.  They could have moved the battery(s) into the console or even into the casting deck.  I suppose foam filled baitwells on the aft would add flotation to support the extra weight too.
They could even add a baitwell up front to counter the added weight.

[Flapilot]

Thanks rick.

1987 and I'm checking on the Honda but it looks like an early 2000's.   There is a bait tank under the lean post. Guess I'll just have to wait and see how it floats.

[wingtime]

Honda four strokes are known for being very heavy. Do a sea trial and see how she floats and where the scuppers are when at rest or when two people stand at the stern. My bet is they are under water with that Honda.

[RickK]

Good advice from Wing plus see if you can get the extent of the rebuild if they did one.  before you take the boat for a test ride look at how it sits in the water empty and then with someone behind the helm.  The livewell is like another person behind the helm.  Then take two people to the aft and see what happens.
The 170 is only good for 2-3 people comfortably or you start getting in each other's way.

[wingtime]

I agree, two to three tops for fishing on a 170. Out for a ride, or sand bar trip, four people. The boat handles fine with that many, they just start bumping into each other.

[boatnamesue]

I'm in the process of checking out a 170 that has a Honda 90hp 4 stroke on the back of it.  Would structural changes needed to have been made when they did the rebuild to accommodate the weight?  Is there any way to check if those changes were accomplished?

I'm going to sea trial the boat to make sure it's not causing wet floors as well. Any suggestions beyond that?

No, no structural changes would have needed to be made.  The boat is plate rated for max hp of 130hp.  Even though the hull is near 30 years old, engine weights haven't drastically changed to make the manufacturer max hp rate erroneous.   Compared to other manufacturers Honda does produce a heavier engine, but 90hp is still under 400lb dry weight.  Honda has never produced a 2 stroke outboard engine, so you can't compare it's weight to the weight of a 4 stroke of the same hp.  However, the majority of the major outboard manufacturers that produce 2 stroke and 4 stroke of the same hp have similar dry weights.  For example, yamaha 115hp 2 stroke is 377lbs and the 115hp 4 stroke is 377lbs (387lbs for long shaft).

If the honda 90hp is around 350-400lbs, which i believe it is, there is no cause for concern of it being too heavy.  It's the same dry weight engine as my engine, Yam 115hp 2 stroke.  At rest in calm water the scuppers will be just above water.  If the '87 model has the removable gutter deck panel and you leave scuppers unplugged you will have water coming in and out.  Then expect water to make its way into the bilge as the boat pitches up and down.  This can lead to a heavy hull if you don't have a bilge pump installed.  Solution:  Keep the scuppers plugged.

 

[Flapilot]

Thank you for all the replies. I was hoping to go see it yesterday but it feel through until the new year. I'll post an update then. 

[RickK]

Take some of these things with you when you go look at it
http://classicaquasport.com/smf/index.php?topic=10634.0

[wingtime]

FYI the Honda BF90 weighs about 377 dry and my 90hp two stroke Evinrude weighs 301 lbs dry.

Hull weight and how wet or dry the stringers are a big factor. Take some pics of her floating. Empty or full fuel tank will make a difference too.

[MarcG]

Timely post since I'm considering putting a 4 stroke on mine when I'm done. I'm getting close to putting in the new floor which will sit on the lip that's left over from the old one. I'll pick up an inch in height for the scuppers there, but moving the fuel tank forward is something I wasn't considering. Other than reinstalling the fuel coffin a foot forward and maybe extending the cutout in the stringer for the filler hose, anything else to consider?  I'm sure there's some math I could be doing (center of gravity, fuel weight, engine weight etc) but I may be over-complicating it.

[Mikerodrig27]

I wouldn't worry about it too much. Unless moving the tank is easy. The johnson 90 that was on my 175 was 315 lbs. That honda isn't a ton heavier.

[snakeoil]

I have installed a Mercury 90 on my 170 Osprey!....its heavy, but I cur down on the size of my new fuel tank and kept it forward!....moved the CC forward about 2 inches.. installed the ball type scupper stoppers on the aft...works just great!