Motor size

Hermanator

Cadet
Joined
Nov 18, 2018
Messages
11
im rigging up a new 16’4” inflatable. Max motor on transom is 40hp recommend and max motor weight of 267 lbs. Here is my delema. Tohatsu 40 hp is 50 lbs lighter than the etec. The 40 Tohatsu TDLI is lighter than the etec 30. So should I have a lighter motor on the transom or does it really matter if your at max on the transom? I’d love some input and opinions. 4 strokes are just to heavy to consider. This is a boat we will keep till it’s dead. Thoughts... thanks in advance.
 

bchaney

Petty Officer 1st Class
Joined
Jul 3, 2018
Messages
246
I'd think as long as you're at our below the maximum weight rating you're good to go. The heavier motor may be a bit slower but probably not significantly.
 

Hermanator

Cadet
Joined
Nov 18, 2018
Messages
11
Max transom weight?

Hi everyone. Very new here and looking for some real world advice. My wife and I just recently purchased a new 16’4” inflatable. The max payload is 2000lbs. The max capacity is 10 adults. The max weight for motor only on the transom is 267 lbs and 40hp. I am not going for max speed, however I do want a motor that can still get on plane when it is weighed down, and still need to be able to troll speed for fishing. The boat is 300 lbs and I’ll have about 500-750 in the boat most of the time, not counting motor weight.
i think I have motor choice down to 2 stroke etec or Tohatsu 2 stroke. However the 40 ho tohatsu is 214 Les and the etec is 260. The 30 etec is 230 is, the 30 tohatsu is also lighter than the etec. Or should I go 30 4 stroke. I’m lost on how to gauge a good balance between motor weight and transom rating with Hp...... thoughts and experience please..
 

bchaney

Petty Officer 1st Class
Joined
Jul 3, 2018
Messages
246
Sounds like both 40hp 2-stroke options are under the transom max weight rating so it just comes down to your preference between the 2 motors. Weight is a factor but I would think other factors are more important like price, reliability, warranty, trolling speed, etc. 46lbs isn't going to prevent you from getting on plane. I messed with the calculator linked below and I doubt the extra weight would affect your cruising speed more than 1mph.

2-stroke vs. 4-stroke is another question. No way would I downgrade to a 30hp 2-stroke for weight savings alone.

https://btb.fishing/boat-horsepower-calculator/
 

Hermanator

Cadet
Joined
Nov 18, 2018
Messages
11
Thanks so much I appreciate the input. So because this is my first inflatable I was unsure if the lighter motor is suggested or if running at max transom weight is ok in an inflatable. How much longer would the transom last with less weight on it over the years. Can I leave the motor always on with an inflatable or should I take it off?

I was set on 2 stroke, however I’m interested in thoughts on running a 4 stroke. What’s better and cheaper for over all ownership?

My last east boat was a 2011 1975 whitewater jet boat so not much exp with out boards in the last 15 years.
 

Sea Rider

Supreme Mariner
Joined
Sep 20, 2008
Messages
12,345
Things to know well in advance before going for any of those mentioned engines :

How many boaters will there be on board most of the times, if only driver, wife, kids, oh boy you've just bought a huge carrier LOL!!.

Will the inflatable be assembled/disassembled, inflated/deflated, the engine be installed/removed every time the combo will be used, will the combo live inflated on top of a trailer, plan going for one ?

Type off boating, pure recreational, cruising, speeding, pulling toys, fishing, sunbathing ?

Can advance you the following : any transom will last for years to come if a high quality glue was used during the assembly along the correct air pressure pumped into each air chamber to achieve a very rigid boat and avoid transom failing due to stress.

Answer those question and will go from there...

Happy Boating
 
Last edited:

Hermanator

Cadet
Joined
Nov 18, 2018
Messages
11
Thanks Searider,

the inflatable will will be used 99% fishing. 50% me my wife and our 2 dogs and 50% me, my wife and our 2 fishing partners with there dog.

I do do plan on leaving the inflatable on a trailer and inflated all year and stored in a heated garage.

Wondering if I should remove motor when not in use, however they seem heavy at 200 plus to be doing that. That’s why I was wondering the stress in the transom if I go max motor or if it’s better to be way lower. Also because of trolling I’m looking for thoughts on the 2 vs 4 stroke option and motor size suggestions.
Thanks for taking the time to help.
 

Hermanator

Cadet
Joined
Nov 18, 2018
Messages
11
Thanks Searider,

the inflatable will will be used 99% fishing. 50% me my wife and our 2 dogs and 50% me, my wife and our 2 fishing partners with there dog.

I do do plan on leaving the inflatable on a trailer and inflated all year and stored in a heated garage.

Wondering if I should remove motor when not in use, however they seem heavy at 200 plus to be doing that. That’s why I was wondering the stress in the transom if I go max motor or if it’s better to be way lower. Also because of trolling I’m looking for thoughts on the 2 vs 4 stroke option and motor size suggestions.
Thanks for taking the time to help.
 

Doh

Petty Officer 2nd Class
Joined
Aug 12, 2008
Messages
187
It's a 300 lb boat. 30 or 40hp will be fine.

A portable tank, so 10-15 lbs on the transom won't make much of a difference also.
 

Hermanator

Cadet
Joined
Nov 18, 2018
Messages
11
Thanks Doh, would a 40 be able to troll slow enough for fishing or would the 30 be better?
 

Range Wharf

Seaman Apprentice
Joined
Sep 21, 2018
Messages
30
I'm new to forum...I have a zodiac 310 solid 10'4.
the tag on the transom says max 20 hp. Being a senior, I was looking at a new 9.9 mercury, being a lighter motor in weight, does one think it would be ok for speed and will it plain..with just me, also at times will have the wife me. I see the 15hp and 20 hp are the same weight. Just wanted some input. Thanks
 

QBhoy

Fleet Admiral
Joined
Mar 10, 2016
Messages
8,286
Have a look at the zap cat posts on the internet. These are high performance inflatables and use similar HP to what you are. Although different boats perhaps...the info on there around engines and set ups is amazing. To many, the Tohatsu is the engine of choice.
 

Range Wharf

Seaman Apprentice
Joined
Sep 21, 2018
Messages
30
Not sure if I posted this request in the right place...or will I receive an email if someone responded.thankyou
 

Sea Rider

Supreme Mariner
Joined
Sep 20, 2008
Messages
12,345
Some issues :

There's a great weight difference between a 2 and 4 strokes OB's in the 30-40 HP range. a 40 HP is too much for that given load. A larger inflatable having more hull length, width lying on water will plane faster with a less HP-OB than if a 40 HP is the max rated for.

Is it still possible to get a 2 strokes OB in your area ? Say a 30 HP Yam, Suzuki will be a good alternative. Usually 4 strokes compared to same 2 strokes ones weights at least 10 + kilos.

An OB of that HP could live sitting on a trailer forever provided that all tubes resting on top trailer are inflated to at least 3.0 PSI for overall best boat rigidity and avoid transom ungluing issues due to OB weight along bad inflation. Will be good to extend the rear tubes bunks supports to where large cone begins along a transversal wooden, metal support for lower transom and attached OB to rest fully there as in pics.


Click image for larger version  Name:	09.JPG Views:	1 Size:	93.0 KB ID:	10681559
Click image for larger version  Name:	11.JPG Views:	1 Size:	95.6 KB ID:	10681560

Will get the max out of the combo if a OB/transom height optimization along a prop maximization are done in that order..

Happy Boating
 

Hermanator

Cadet
Joined
Nov 18, 2018
Messages
11
That’s awesome info. Ok I feel good with either direction I go then. Now it will come done to price..... I’m thinking boat show will be the best time to buy this winter. Thoughts?

Love the trailer, I’m converting my flat deck to haul the inflatable so the transom will be supported while in transit.

Thanks SeaRider
 

Sea Rider

Supreme Mariner
Joined
Sep 20, 2008
Messages
12,345
You're Welcome Hermanator,

If with a flat trailer front to aft will need to deflate lower keel each time the boat is put on trailer, inflate once on water, deflate when out of water before putting back on trailer and so on each time the combo will be used.

See if possible to modify the flat trailer to add a middle open section the length of the entire inflated keel as in pic so to have the keel inflated at all times while tubes rests properly on side bunks.

A boat show will be a good place to search and buy any OB brand of your preference. If no 2 strokes are available go for any 30 HP 4 strokes ones say, Tohatsu, Mercury, Yamaha, Suzuki, if carbed much better. 25 and 30 HP ones weights same as both are same CC powerheads. If budget can hold go for a 30 HP, when you get tired of that combo and plan selling it a 30 will be more suitable if future owner plans boating with more boaters than as right now.

Just a thought, would it be possible to return that large carrier and trade it for a 420-460 size powered with any 30 HP-OB of your particular preference ?

Happy Boating
 
Top